Mac USB keyboard sometimes works, sometimes doesn't - how do I reset it?

Mac USB keyboard sometimes works, sometimes doesn't - how do I reset it?

I have a MacBook Pro with an external generic USB keyboard / hub. The keyboard stopped working - usually. If I unplug it and plug it back in a few dozen times, the keyboard usually starts working again. It then continues working with no problems until I unplug it again. I have a USB mouse plugged into the keyboard's USB hub - this always works fine.