The term "be on air" typically means to broadcast live or to be live on radio or television. Antonyms for this term might include "off air," "not broadcasting," "pre-recorded," or "not live." These terms suggest that the program or event is not currently being broadcast or that it is not happening in real-time. For example, a pre-recorded TV show would not be considered to be "on air," since it is not being broadcast live at that moment. Similarly, if a radio station goes off the air temporarily due to technical difficulties, it would no longer be considered "on air" until the problem is resolved.