Since the inside of your case is below the temperature of the air in the room, its not surprising you get condensation on the outside of the case. But thats really nothing to worry about. It will only happen outside the case.

One thing to be careful of though - it IS possible to get condensation inside the case if you run your cooling setup for a while without the computer on, then open the case. Then the parts inside will be cold and when the warmer air from the room hits the parts, you'll get condensation. So just make sure you don't run the cooling system while the computer is off.