Is riding a motorcycle like riding a bicycle?

Mostly yes.  The feel is different - more stable, softer, and almost lazy compared to bicycles, but as a concept it is similar.  You're still learning the feel of a particular bike, and calibrating your inputs to how it responds.  In my opinion, this process is much more instinctive and clearer on two wheels than four.

I disagree somewhat.  Riding a bicycle is more like paddling a CANOE than riding a motorcycle.

Edited the canoes out of the original post just in case OP wants an answer. 

(not) WilD (Matt) said:

I disagree somewhat.  Riding a bicycle is more like paddling a CANOE than riding a motorcycle.

I can agree with this. 

Some of the same principles apply, and knowing how to ride a bicycle is a better start than not knowing how to ride a bicycle, but they're still very different experiences.  Compared with a bicycle, a motorcycle has:

• More weight.  Your body weight is probably ~5x more than the bicycle you're riding.  A motorcycle will weigh anywhere from 2x to 10x your body weight.  This means that it doesn't respond nearly as much to just leaning; riding a motorcycle requires understanding how your steering input actually controls the machine.  Also, if you lose your balance while at low speed or stopped, it's very hard to regain it and catch a tipping motorcycle.
• Bigger wheels and tires.  This means you have more traction, and more stability when moving (more rotating mass = more gyroscopic effect).  30 mph on a bicycle is kinda scary.  100 mph on most motorcycles feels like a casual Sunday drive.  This is obviously a good thing since highway stability is nice.  However it can be very deceiving and give a false sense of confidence.
• More power.  The acceleration, even from a 250cc, is addicting to new riders.  But of course power means speed which can mean trouble.  Also you have to give consideration to traction available for acceleration, since you don't commonly spin the rear tire on a bicycle but it can happen easily on a motorcycle in wet or dusty conditions.

My advice would be to find a friend with a low-end motorcycle and see if they can teach you the basics.  A MSF basic rider course is also a great place to start, and they start at square one and build the fundamentals from there.  If you do buy your own bike, buy something small (<400 cc) and cheap that you can get comfortable on and take your time learning.  A Ninja 250 is a fantastic starter bike and they can be had for $1500 so you won't feel bad if you drop it.  Some people will bash 250 cc bikes, but those are not people whose advice you want to listen to.  Don't outride your experience level, and don't be afraid to ask questions.

Life on a motorcycle is an amazing thing, and doing so safely ensures you'll be able to enjoy it for years to come.

Anyone who bashes a 250cc bike or smaller is an ass who repeatedly had the crap scared out of them by their "beginner" 600 sport bike and somehow they didn't end up with head trauma and think that's how it should be done.

If you really want to see a good monolog about small bikes, search out Regular Car Reviews 250 Ninja review on YouTubes. It really will sell you on why smaller is better.

Get a cheap dirtbike to bash around on and learn what the controls do.

 So many freeze the at the 1st sign of trouble and simple crash with the throttle wide open and their feet dragging.

 Don't be that guy on the street,learn in the dirt 1st and you'll most likely stay alive and rash free.

The OP posted here once, back on 12/26...I suspect they won't ever come back to read any replies.

Still might be a good read for anyone else who is wondering.

No one mentioned countersteering yet - that was the big thing that threw me off guard my first time riding a "big" street bike (Honda 750 I think). You mean you need to turn the bars left to go right...whaaa?

If you know the basics of countersteering going into  your first motorcycle ride, things will go a lot smoother I suspect.

The effect of the weight cannot be overstated.  I've been riding dirt - offroad and MX since I was 9-ish years old.  My current YZ250X 2 stroke weighs about 225lb or so with the armour I've got on it.  The difference in feel and riding technique between my mountain bike and my dirtbike is monumental.  But when I've been riding my Kat 750 for a few weeks and jump back on the dirtbike, the YZ feels like a mountain bike - and I'm not really exaggerating that much. 

Countersteering is a thing.  It must be learned and become instinctive through conscious and repetitive practice in order to ride on the street and avoid death.  Dirt bikes for the most part (in an offroad, trail type setting) really steer with legs and body weighting.  500lb street bikes do not.