Does ur mobo has a feature such as Dynamic Overclocking?

Dynamic Overclocking Technology is the automatic oc function. It is designed to detect the load balance of CPU while running programs, and to adjust the best CPU frequency automatically. When the mobo detects CPU is running programs, it will speed up CPU automatically to make the program run smoothly and faster. When the CPU is temporarily suspending or staying in the low load balance, it will restore the default setting instead.

If this the case for u..just disable such feature in BIOS. If it is enabled, it will be powered only when user's PC need to run huge amount of data like 3D games or the video process.

If ur DFI board really has this feature...this is the most relavant explanation for ur problem.