A muscle doesn't have to be sore to have been worked out. DOMS varies greatly from person to person, and from workout to workout.
If you are doing very light weights (like those used in the Firm '4-limbed aerobics' workouts), then I'd say that you could work the same muscle group again. Doing so is like doing Freestyle training, the goals of which are to gain endurance and strength without gaining any size (or even losing size).