I'd say just don't put the tank super close to the computer. I would think a few inches away would be fine as long as the noise doesn't make things vibrate or can be heard super easily in the next room.
I've only seen my fish react to sound once, and it was when I put an earbud from my headphones directly onto the glass right beside his head. Although he doesn't like the drawer below him moving his tank or having my desk chair whacking the table!! :P
I would try your fish tank there and if you notice him reacting negatively to the sound, move his tank elsewhere :)
I'm pretty sure fish can hear well, but I don't think most sounds bother them.