The folks over at CinemaBlend tracked down a Star Trek Into Darkness press conference video where director J.J. Abrams was (naturally) asked a question about the other Star franchise he’s working on. Specifically, whether or not John Williams would be back to score Episode VII. Skip to 8:14 to get right to the question.
The relevant quote: “For Star Wars it’s very early days … but I believe that … John Williams will be doing that film, because apparently he was there long before I was.”
Remember, though. This isn’t official confirmation and it won’t be until you hear it from Disney or Lucasfilm.