There could be a number of reasons for this behavior:

1. He's starting a shed and trying to break the skin around his face
2. He has a respiratory infection and is trying to swipe the mucus out of his mouth
3. He's got something lodged in his mouth and is trying to get it out (aspen or bark bedding is most likely if this is the scenario)
4. He has mites and they are irritating his mouth and/or eye