Over heating problem I am using Samsung Galaxy S II GT-I9105.
Lately I installed a game called Mini Warriors. At game play, my Mobile gets heated.
The weird thing is, when I touch the battery, it is normal. But the area surrounding my camera is hot. I know resource hungry apps like games heat up the mobile. So, is it normal?
Yes, it is normal.  A resource-intensive app like a game may cause the phone to heat up. The phone should cool down after you stop playing.

The battery is unlikely to be the component getting hot (unless it's defective, of course.)  According to the Galaxy S2's teardown, the component near/behind the camera that could be the culprit is the CPU.  Phones and tablets don't have active cooling systems like fans inside desktop computers or laptops, and usually don't even have passive cooling like heatsinks.  This means that for cooling these chips rely on whatever ambient environment there is - usually nearby components (like the camera in your case) or sometimes the case of the phone itself.  Most modern phones include CPU/GPU temperature sensors that automatically slow the phone down when a certain temperature is reached in order to avoid damage.