as long at its under say the 35c your ok.
If you computer has an AMD Athlon I would advsie to add a rear 8cm case cooling fan, also check to see if other internal cooling fans like on AGP card & the Heatsink over the CPU is spining.
Excessive dust will not help in blocked fans. Switch off machine and clean carefully with a Can of the Air Dust spray cans. Do not spray too much as it will freeze things.