Check the visibility options in the scene and environment sections of the 3D hierarchy tree. It's somewhere in there (seems those questions always pop up when I'm not on my CS6 machine and my memory is failing me so I can't verify) .
Generally speaking, you can click on a tool in the Tools Panel other than the Move Tool and the ground plane will be hidden.
But if you want to be able to rotate, etc. without seeing the ground plane you'll have to do as Mylenium has suggested and look for a way. I only see a way to change the color in the Preferences, not to turn it off.