many motherboards automatically overclock a small amount. Go into BIOS and turn it off. If your CPU is super-locked, you won't be able to use this feature, so just turn it off.
My MSI K7N2 delta 2 platinum board does this. It will not overclock with the current CPU. The previous CPU I was able to overclock.
Just remember, overclocking is risky and will void any warranty on your CPU.