Like keith12 said, we need your specs to know. It may or may not. If you have a sandy/ivy bridge i5 then ocing will likely do little to nothing. For example, I just got a second 7870 and was playing tomb raider last night. My 3570k cpu usage never went over 40%. An OC would be pointless for that game.
1/ Your game is heavily CPU-intensive and doesn't need much graphic power ( some MMORPG games, like TERA for example ).
2/ Your CPU is bottle-necking the GPU ( full load on 1/2/3/4 cores of the CPU ( depends on how many CPU cores that game you play can ultilize ) but only 80% or less GPU usage while gaming ).
Then yes, OCing the CPU will help improving the FPS.