Ben Affleck testifies on Capitol HIll on Dec. 19. (Susan Walsh/AP)

Whoever replaces Sen. John Kerry (D-Mass.) next year, it won't be Ben Affleck.

The actor and director faced some speculation that he would compete for the seat, which will become vacant, assuming Kerry's nomination as secretary of state is approved by the Senate. In recent interviews, Affleck ducked questions about a political career. But he ruled it out in a Facebook post on Christmas Eve. 

"I love Massachusetts and our political process, but I am not running for office," the Affleck wrote. "We are about to get a great Secretary of State and there are some phenomenal candidates in Massachusetts for his Senate seat. I look forward to an amazing campaign."

Affleck said he would continue working with Eastern Congo Initiative, the nonprofit he founded in 2010, and on other national and international issues. He was recently in Washington to testify before the House Armed Services Committee, asking the U.S. government to take an active leadership role in helping end the war in the Congo. 

Likely Democratic candidates include state Attorney General Martha Coakley and Reps. Michael Capuano and Ed Markey. A recent poll found that Sen. Scott Brown (R), defeated in November by Democrat Elizabeth Warren, leading all potential challengers.