That is intel speed step technology. It will reduce the speed of the cpu to save power if there is less load on it. reduction in cpu speed results in lower voltage and less heat and power consumption.
When you will put load on your cpu, like do 3D rendering for example, speed step will push it back up to its full speed.
your cpu is working fine. do not worry. my core i5 2400 has default speed of 3.1 GHz and turbo of 3.4 GHz yet as I type this post, it is running at 1.6 GHz
-satyam