[Mauzen]

Virus keyboard input (aka software keyboards) dont really care if the keyboard is plugged in or not. Might be a way to avoid being detected by scanners, but simulating hardware keyboard input is an even more invasive action that will rather be detected.
I doubt thats some kind of malware, probably your keyboard is just malfunctioning. Ive once had a wireless mouse/keyboard combo. The cursor jumped around when pressing certain keys, and the keyboard produced input when pressing mouse buttons in a certain way.

Alternatively, your keyboard might be possesed by a ghost.