Its ok if it is not charging, my Asus K55A does it all the time, it shows at "98% charged, Not charging" its fine. Generally when that happens, its a error with windows predicting how much battery percentage is actually on.
IF your really concerned, plug in to a full charge and discharge to 6-10% for two or three times, charging for 6ish hours between(or a night) and that should get make the percentages more accurate.