The phrase "am on the air" refers to someone who is currently broadcasting or being broadcasted, usually through radio or television. Antonyms for this phrase would include "off the air" or "not on the air", which both indicate a lack of broadcasting activity. Other antonyms could be "silent" or "quiet", which suggest that there is no sound or noise coming from the station, or "offline" or "disconnected", which imply that the equipment or network is not functioning properly. In any case, the antonyms for "am on the air" all convey the opposite state of being and indicate a lack of ongoing broadcasting activity.