Depends on what band you'd be running. If it's far enough away in freq, no problem. For example, a 440 rig should be no problem at all. Might be a bit dicey if you are running 10 meter. They are next door frequency neighbors and the energy from one will bleed into the other. If it's strong enough, there may be enough energy to damage the other radio's receiver.
You'd have to have the specs on the units and antennas, and do some calcs to be sure, but offhand, I wouldn't recommend running 10 meter that close to a CB.
But that's just off the top of my head. Maybe someone who has done it can chime in.
If you have a footwarmer on either one, even without doing any calcs I'd say you'll fry a front end.