Overheating would imply it's heating to a capacity where it shuts off or throws a warning to the user.
normal operations of a CPU can vary, for the most part day to day use of a CPU can throttle slightly above idle speed and work well, however there are times when a user does something that requires a CPU to do some serious calculations; for the most part the CPU will have demands on it that will cause it to work harder, producing more heat and the system will try to assist with cooling and venting (e.g. fans running faster).
As long as the CPU is not causing a reboot, a crash or a shutdown it's normal to experience your CPU adjusting itself to the needs of the user.
If something more specific is happening you keep an eye on your activity monitor to determine what the CPU is doing when it's "overheating", and you may wish to perform a hardware test if you are concerned with this behavior to see if there is something wrong with the system.
Using Apple Hardware Test - Apple Support
if a problem is found you should contact Apple.