Yes, it is meant to do that, when Speed Step is enabled in your UEFI/BIOS. which it must be. It's a standard Intel power saving feature on their CPUs. Under low load or idle situations, the CPU shifts its speed down to save energy and produce less heat. As soon as more processing power is needed, the CPU cranks up to it's full speed. So all is well.
Are you referring to the Core Speed in CPU-Z? If it is, it should be near the max speed of 3.8 Ghz with CPU-Z settings set at default.