Ios7 mute/end call problem.

Little problem with ios7 on my 4s. When I'm talking on the phone it touches my face, and goes on to speaker/mute or sometimes hangs up. I don't think this has ever happened on my 3GS ios6 and 4s on ios6. Does anyone else get this problem with ios7? Is it a bug? or is there somewhere in the setting that I can fix this.