CPU speed stuck at 798 MHz

I am quite new to Ubuntu and Linux world, Can anyone help me to increase the normal CPU speed of my processor? It is a i5 2.3 GHz and for some odd reason is stuck at 798 MHz, that’s why I installed linux and stopped using OS X, Ubuntu feels faster but is still not using my processor at its normal speed. I tried different distro to increase the governor performance but even on Performance mode clock speed still at 798 MHz. Can any one help me through this issue? Can it be done from BIOS?