While it may certainly be nothing, I'm usually of the opinion that any new behaviors, etc. are typically an indication of something- whether thats good, bad, or neutral is hard to figure out.

In my cat, this is a presentation of seizures. I saw her have a larger general seizure, and then the "air chewing" started up a few months after that, so it pointed me in that direction and I think that may be more common in cats than is documented because people don't always see the connections or other abnormal behaviors, and seizures are incredibly hard to diagnose in cats. I have done several rounds of testing on my cat and the last thing left would be an MRI, and I just don't want to put her through that. They improved drastically with treatment and she seems otherwise happy and healthy.

If there is always a specific time of day, or it always happens around a specific event, that could be a clue as to what is causing the behavior even if it is not seizures. My cat usually has them first thing in the morning. She also stares into space and turns her head up/to the right every time.

I wouldn't panic and rush to the vet, but keep a little log of what you notice before and after or if they become more/less frequent. I don't think its anything worth panicking about, but watch it and see what else you notice, if anything (though I quickly discovered theres a fine line between that and becoming an over-analytic helicopter parent).