No, Facebook won't notify the person you've unblocked them. However, there are some scenarios where they might suspect they've been unblocked:
Keep in mind that if you block someone and then unblock them, you cannot block them again for 48 hours . If you are trying to "peek" at their profile quickly and re-block them, you will be stuck unable to block them for two days. will someone know if i unblock them on facebook
When you unblock a person on Facebook:
Facebook will never send a “So-and-so unblocked you” alert. The only way they’ll know is if you actively interact with them again after unblocking. No, Facebook won't notify the person you've unblocked them
To unblock someone on Facebook:
When you block someone on Facebook: