Home Forums Peripherals & Multimedia Peripherals erratic keyboard behavior

I am getting kind of desperate with this problem. When working on Word 2011 documents, my computer sometimes starts typing squares on its own. It may stop after a few lines but most of the time, I have to click with the mouse several times or simply save file and exit. This behavior may return after quitting Word. I have changed the mouse to the new Magic 2 from Apple, and removed the USB extension cord that connects the keyboard to the computer, also switching to another USB computer port. Additionally, sometimes on the desktop or in Outlook I click on an item but the highlight does not occur staying on some other icon. Relaunching Finder helps temporarily. I am on the latest El Capitan (11.2) and working on a MacPro 2010. All tests of the computer come out with nothing wrong. Restart does not help. All key options in the Accessibility control panels are unchecked. Internet forum search came up with some similar issues but no good remedy was suggested. Have no idea whether this is software or hardware issue (like old wired keyboard). Suggestions are much appreciated.