It can be even worse than I suspected. Turns out, even your mouse dongle can be used to inject keystrokes: https://media.defcon.org/DEF%20CON%2024/DEF%20CON%2024%20pre...
I recall when the first Logitech wireless keyboards came out.
Me and a friend were at a regional lan party, and he had one of those keyboard. As we soon learned someone else in the locale also had one, because he would ever so often get random inputs on screen...
Yeah, watch out with those, because a wireless wire is about accurate security wise too. Typically the proprietary dongles have very little security wise.