I have been sick with bronchitis and on antibiotics . is it ok to exercise?

Yes: But acute bronchitis rarely requires use of antibiotics. It is generally a viral illness which will resolve on its own, with antibiotics not only providing no benefit, but actually creating potential risk. If, however, you had adult onset pertussis (whooping cough), antibiotics would be useful. You can certainly exercise but would be careful to stay well hydrated and not exhaust yourself.