I've seen a few trucks with the bed off because obviously someone was working on it - so long as you have your lights and tag mounted and the lights are working it should not be an issue. If you want to be sure, flag down a local peace officer and ask, or call your county clerks office to ask, or enquire at the local DMV (or MVA, or whatever the heck we call it...).

It isn't unusual.

There was a truck in front of Haddads in Munford a week or so back with no bed on it. Consequently I could see the details of the airbags, compressors, lines fittings and solenoid valves that were plumbed under there....

It was almost laying it's frame down on the pavement!