Stepping back one. Are you even sure the reading is real. If the PSU doesn't provide a reading whatever you see is meaningless.
Next time the computer has been off for an hour turn it on and check the readign right away. Check it again after 20 minutes of surfing then next time you game check it right after a gaming session. The readings should increase since the load on the computer does. If it's always the same there is no sensor or if it's an expensive add on supply it could have a speed controlled fan that regulates the temperature.