How to Unblock a Person on Facebook
Facebook allows you to block any other user of the site. When you block a user, that person is removed from your friends list and can have no interaction with you. If you decide that you want to be friends with the user, you can unblock them. Unblocking the user will not add them as a friend. You will have to send the user a friend request separately.
Navigate to the Facebook website at www.facebook.com in any Web browser.
Log in to your account.
Click on the "Account" drop down menu at the top of the page.
Click on the "Privacy Settings" menu option.
Click on the "Edit your lists" link under the Block Lists section at the bottom of the page.
Click on the "Unblock" link next to the name of the person you want to unblock in the Block users section.