Keep in mind that I'm not relaying any voltage or current. Just closing a circuit.
If there wasn't any electricity flowing through it, then what would be the point of closing the circuit?
If it's a keyboard, then when you press a key, it completes a connection and current flows through. I assume you are trying to bypass this through the Arduino to simulate keypresses?
[edit]Doh. Didn't see your post Osgeld :P. This is essentially a repeat of it..Ah well ;D[/edit]