The actor posted a message on Facebook Monday that he's not quitting his day job.
He wrote: "I love Massachusetts and our political process, but I am not running for office."
Affleck grew up in Massachusetts and was rumored to be considering running for Senator John Kerry's seat if he is confirmed as Secretary of State.
The actor stirred speculation with a noncommittal answer on CBS' "Face the Nation" Sunday about whether he would seek the seat.
Affleck said he's happy being involved from outside the government.
He says he will continue his work campaigning for aid for the Eastern Congo, veterans and fighting domestic hunger.