Do you mean Battlelog? Battle.net is another game company's site which does not interface with origin.
To accept a friend request in your PC Origin client, install the client, log in with your Origin account that you use for Battlefield, and then in the top right hand corner hit the button that looks like a person. This will open the friends list and at the top of the friends list you will see a list of friend requests. Either select "accept" or "ignore" under each person who has sent you a request.
You can also accept or reject friend request by logging into Battlelog.
