Anderson's representative would not comment on the reason or any particulars of the divorce. Anderson and Rock, whose real name is Robert Ritchie, each cited "irreconcilable differences" in their divorce filings in Los Angeles County Superior Court.
"Yes, it's true," Anderson wrote in a brief statement on her Web site. "Unfortunately impossible."
A message left with Ritchie's attorney wasn't immediately returned.
The relationship between Anderson, 39, and Ritchie, 35, has been a turbulent one since they became engaged in 2002. They broke up the following year, but later reunited and held several wedding ceremonies over the summer.
They were wed in late July near St. Tropez, France, and again at a courthouse in Beverly Hills on Aug. 3. They also tied the knot in an Aug. 17 ceremony in Nashville, Tenn.
The pair filed separate divorce petitions, about an hour apart, early Monday. Anderson reported their separation date as Nov. 21; Ritchie said it was Nov. 26.
First word of the split was reported by "The Insider" syndicated news magazine.
Anderson's spokeswoman, Tracy Nguyen, confirmed earlier this month that the actress had suffered a miscarriage.
The actress has two sons, Brandon, 10, and Dylan, 8, from her marriage to rocker Tommy Lee. Ritchie, a Michigan native who owns a condo in Nashville, has a 13-year-old son, Bob Jr.
Anderson appears in the "Borat" movie and has been filming "Blonde and Blonder." Rock released his latest CD, "Live Trucker," in February.