Facebook annouced in a recent blog post that they intend to make our page likes more meaningful. What they mean by this as that, in future, the likes your page has will only be counted from active accounts.
Facebook will remove likes from memorialized accounts and deactivated accounts. Conversly, accounts that were previously deactivated will automatically re-like your page, if they are reactivated at some stage in the future.
All in all, this means that the number of likes your page has, is a closer reflection of users who might actually see and interact with your page.
This behaviour isn't entirely new either, since Facebook already removes likes and comments from the individual posts; so this update is just bringing that behaviour in line for pages.
It all kick's in this week, starting 12 March, Page Admins will see their Page Likes dip as a result of these changes. But don't worry - these likes are already inactive and do not interact with your page anyway. Be prepared, and don't panic if you see a dip.