The term "are on air" refers to something that is currently being broadcasted or aired. Its antonym, "are off air," means that the transmission has ended or the communication channel is no longer active. When a program or channel is off air, it means that it is not currently available for viewing or listening. Another antonym for "are on air" is "are not broadcasting," which indicates that the signal is not being transmitted at all. These antonyms are commonly used in broadcasting and media industries to describe the status of different channels or programs.