[hocus pocus]

While clenching your jaw can be a normal reaction to stress, it could be self-harm. One way to look at it is that anything you do with the intention of causing harm to yourself can be considered self-harm. Do you do it with the intention of harming yourself or do you feel as though it's more of just a reaction?

If you'd like to stop clenching your jaw, maybe you could stop doing it as soon as you're aware of it. You could also develop other coping techniques, such as breathing techniques or carrying something around, like a stress ball as it has been mentioned. You could try chewing gum or sucking on mints and hard candy to see if that helps, because it is a motion in your mouth like clenching your jaw is.