Welcome to Android Central! Does this persist after a reboot? If so, some other app you installed might be interfering. Try booting into Safe Mode, which temporarily disables all 3rd party apps. How to boot the Galaxy S3 into Safe mode?
If the problem disappears in Safe Mode, then something you installed is causing the problem. You may have to uninstall apps one by one until the problem disappears. If the problem persists in Safe Mode, then it's more likely to be a hardware or firmware problem.