How long is a peice of string?
Could be a number of things:
1) Your case is so small airflow is suffering as a result
2) You've a stock cooler in a small case, airflow suffering as a result
3) Your cooler is naff
4) Depends on your make of CPU - some run warmer than others. i7's for instance run at 40C at stock with good airflow. If your case is small then that number would of course be higher.
So the baseline is:
More info please. What CPU is it, what do you have cooling the thing, what is your case and do you have any fans in that case moving air around?