Do you mean that it says something like:

Unread Messages: 153

If so, that means that there are 153 messages on this message board that you haven't read yet. In order to get rid of that, you have to read all the messages on the message board, though in the next version of this site (due out within a couple of weeks), you will be able to mark old messages as read so you won't see that.

Hope that helps,
-dr