This can be a tricky question, but there are a few things that you can do to figure this one out. These are easy things and can be done in the space of a few minutes.
Company Policy
First and foremost, you should check to see if your company has a no gift giving policy in place. Some of them do. If your company has this type of policy then you should definitely NOT give your boss a Christmas gift.
No Policy
If your company does not have a no gifting policy in place then they may have a prescribed method for gifting. For example: you may work in an office where names are drawn at random and that is the person to whom you give a gift. There may also be a set price limit that gifts cannot go beyond. In this case, if you do not draw your bosses name then you might not want to get him/her a gift but instead can get a card.
If your company does none of those things then you can get your boss a gift. There is one other thing that you should keep in mind though. Some religions believe in Christmas, some don’t. If your boss is of a religion that does not do the Christmas thing, then I would advise against getting him/her a Christmas gift. It could be offensive to your boss if you do.
If you do decide to get your boss a gift, make sure that it is tasteful and fitting to your boss.