Bullock, 45, was seen at the home of Gabriel Brener, the head of the Brener International Group, LLC, a private investment firm based in Beverly Hills.
According to a friend of the actress, the visit was strictly personal. "She's not there on business," says the pal. "They've been friends for decades."
Brener and his family were guests at Bullock's 2005 wedding to Jesse James near Santa Barbara, Calif. The Oscar winner has also vacationed with the Breners on numerous occasions, including a 2001 trip to Greece.
"She spends a lot of time at his house," adds the friend.
This marks the first time Bullock has been spotted in public since she moved out of the family home on March 15. Meanwhile, James, 40, is seeking help at a treatment facility "to deal with personal issues," his rep has confirmed.
Get a sneak peek of this week's issue – Sandra Bullock's divorce dilemma, new Jolie-Pitt twin photos and more – which is on newsstands Friday