Clicker keeps getting locked / stuck

Regardless of if I'm using the keyboard or the mouse, my clicker keeps getting stuck on my MacBook Air. It will highlight block of text on, for instance, a web browser. It happens sporadically, but usually a few times a day. I cannot get to Force Quit or any of the other commands to respond. I have to shut down the Mac and restart and most of the time it returns to normal for awhile. It is not a mouse issue.