It may just need some time to update itself, but try this and see if it helps...
Open the Facebook app, click the "..." on the app bar in the lower right corner to open the settings menu, swipe right to the "notifications" page, change the drop down to "no notifications".
You can either leave it that way permanently or change it back once the notification clears. Personally I leave it off because I think it was interfering with the me tile notifications. Also, it looks stupid with that black circled number in my opinion.