DICE's Daniel Martos has confirmed that EA's online service Origin will be required to play Battlefield 3 if it's bought at retail. During the Alpha testing, online activity was managed through Battlelog, so it's unclear if downloaded versions will require Origin as well.
It's not too big of a surprise. Especially with EA trying to push Origin as an online distributing and social service. Valve requires all games purchased through Steam to have the client up and running whilst playing.
EA also recently confirmed that Battlefield 3 will not be available through Steam, courtesy of Valve's Terms of Service, but will be available through other notable online distributers, including Origin.