Weird green fps counter in top left hand corner of screen

A green number that is probably my fps is in the top left hand corner of my screen. I couldn't attach any pics because when I took them, the number didn't show! Its really annoying. My show fps option is off. I am using Optifine, but that's not the issue because it shows in vanilla too. And its not some computer application because it only shows in minecraft. Please help me!