Is there any damage in doing this?

It's only gonna be for practicing in my room, no gigs or anything, so it's not going to be used at any huge volumes.

Any ideas?
-A Guitar
-A Bass Guitar
-amps for BOTH of them!!

(who cares?)
If you keep it fairly quite it shouldn't matter. It's the lower notes that would hurt it. It would be like playing a bass through a guitar amp. The speaker isn't made to handle the lower frequencies.
"There is more stupidity than hydrogen in the universe, and it has a longer shelf life."
-Frank Zappa

"Where words fail, music speaks."
-Hans Christian Andersen
The keyboardist from Deep purple ran his through a Marshall stack, So i don't see why not.
Marshall JCM 2000 DSL 50.
Ibanez SZ720FM
Boss MT-2 MetalZone
Boss GE-7
Zoom II Effects Pedal
ive got a 15 watt marshall that i use for my keyboard after i got my stack. it works totally fine and also its come through alot louder than the actually guitar does and cleaner
The frequencies you can get out of a keyboard are probably no more harmful than plugging your iPod through your amp. My friend did that for a few hours, and it was loud, so I doubt there would be a problem.

On the other hand, don't plug in a bass.
I'm a Fire, and I'll Burn.Burn.Burn.
My friend plays his bass through a guitar amp, still works perfectly fine.