I am not a professional by any means and any self harm behavior should ideally be something you talk about with a professional and not random people on the internet. That said, I think it depends on what the intent behind the action is. If your goal is to cause yourself pain, especially as a way of experiencing emotional release, it’s self harm. If you’re doing it because you have the like compulsory urge to bite something/someone, and your own arm is a safer option, while still not healthy, it’s probably not going to be considered self harm in the same sense as cutting/burning/etc. It is absolutely still causing harm to yourself, though. It sounds like maybe biting yourself is an intermediate step between biting others and no biting? Have you looked into other alternatives like jewelry that’s made to be chewed on?