There are several possibilities, ranging from loose cable connection to water damage, or possibly a corrupt keyboard driver (though not likely). If you have a USB keyboard, plug it into the laptop and see if the issue occurs with it. You can try going into the device manager, uninstall the driver for the keyboard, abd then restart the computer. You can also try using compressed air or vacuum out the keyboard to see if it helps. What you may wind up having to do, though, is take apart the laptop and the the keyboard out, clean what you can, reseat the cable firmly into place, and test it out. If the issue persists, you may have to replace the keyboard.

unplug the keyboard and blow any dust of the connector and reconnect it FIRMLY