I believe this would be a judgement call on the part of a police officer. If you were wearing a ski mask because you were freezing, the heater was broken and you weren't driving like an erratic fool, I'm sure it would be fine. On the other hand if you were wearing something that scared other drivers into crashing into trees or obstructed your vision to the point of doing the same, you might have a long night at the police station ahead. Or maybe the ER.
it depends on the mask. if you can see the face of the person whos driving then its fine. that is both incase you are a criminal and also so it doesn't obstruct the vision. but think about motorcyclists, there helmets are considered mask yet its still legal
Are you talking about a cheesy Halloween mask covering your face and most of your eyeball or a mud mask to make your skin glow? Either way, if you drive with it make sure you take it off before you go into a bank!!!