Most circuit training programs blend weight-training exercises for your entire body with full-body cardiovascular exercise, moving you quickly from one exercise to the next with minimal rest in between. Because of this, it's not a good idea to do circuit strength training every day. Your muscles need at least 48 hours to recover between workouts -- sometimes more, if you're still very sore once that 48-hour clock elapses.
Video of the Day
A Theoretical Exception
There's nothing wrong with doing cardio on back-to-back days -- as long as you give yourself occasional rest days, can maintain good form and don't feel any ill effects such as joint pain or lasting soreness. So in theory, you could do circuit classes on back-to-back days, too, if you were to limit the scope of the strength-training elements -- say, upper-body workouts one day and lower-body workouts the next.
In Practical Terms
But in practical terms, working all your major muscle groups in one session is inherent in the very concept of circuit training. So unless you're in a very specialized program, it's best to resign yourself to taking at least 48 hours of rest -- or in other words, skipping a day -- between your circuit-training sessions.