Intel i7 / i5 series CPU provides Intel Turbo Boost technology. When this type of CPU is installed, system will enable this feature by default BIOS settings. Therefore, CPU frequency showed during POST is higher than its specification.
If you want to turn off this feature, please refer to user's manual, to enter"BIOS \ MB Intelligent Tweaker(M.I.T.)\ Advanced Frequency Settings\ Advanced CPU Core Features", to disable"Intel(R) Turbo Boost Tech" item.
For more information about Intel Turbo Boost technology, please refer to Intel official website for Intel® Turbo Boost Technology frequently asked questions.