Facebook will be removing inactive accounts from Pages' likes as of yesterday. This is nothing to worry about, unless a significant percentage of your likes come from deactivated or memorialised accounts. This may be the case if you've recently taken on a long-neglected Facebook Page or if you've ever bought page likes.
The reason behind this move is to make your Facebook insights data more meaningful - besides, other than a boosted ego, what use are 100 likes if they don't engage?
If you'd like to find out more, read our previous post on why numbers aren't everything.