Leenia, a keyboard, when unplugged, is simply a piece of plastic and metal, and can do no harm to a computer whatsoever.

As for the dishwasher, I have never tried it; the water may be too hot. Rinsing with a detergent is a better idea; use a shower afterwards to remove the detergent and any dirt left over.

If you replug the kb while still wet, it won't function properly and may indeed cause some harm.

A vacuum cleaner is an unplugged computer's good friend, inside and outside. Dust is the enemy. (We had that topic before, Leeneia. May our readers form their own opinions.)