It can depend on what is occurring with your particular machine. If it is in a hot room and the fans are running constantly then I would definitely say it is over-heating. It could also be that a process or program running on your computer is taking up a lot of CPU and the fan on your CPU is kicking in.
However, to get specific with your situation as you describe it. Make sure it has air flow. If it is a tower/desktop you could try running it with the case off for a little bit. Add a few fans to it to increase the air flow and make sure the power supply unit is dust free. Lift it up off the floor a little bit this will help mitigate dust-bunnies, and take it out of any of those wooden CPU drawers that are common on certain desks.
If you're using a laptop, make sure the laptop fans are not covered when you set the laptop on a desk. I've seen a lot of good laptops place the cooling fans on the bottom where it will get no air flow and totally ruin the laptop after a while.
A program liked Everest (I believe this is the the official website http://www.lavalys.com/community/blog/2010/03/ever... can help tell you what the temps are for certain system components you're using and where to place fans. Even an external fan pointed at the machine can sometimes help.