Hi
Yes beardies do brumate.Its sometimes hard to tell if something is wrong or if they are just brumating.Is he losing weight?How old is he?Are there any other symptoms.Here is a link to a great article written by one of our members here: http://www.beardeddragon.org/articles/brumation/
It should help you understand brumation better as well as how to treat your beardie during this time.