Hashemi, a strong supporter of Mir Hossein Mousavi, the the main defeated candidate in the June 12 presidential election, was released late Sunday, it said.
Iranian newspapers reported that she had been arrested on her way to take part in an opposition rally which ad been banned by the authorities.
She was arrested with four other Rafsanjani family members, the Sarmayeh newspaper reported, quoting Fars as saying they were detained for their "own safety."
Fars said the other four were also freed on Sunday.
Hashemi, a political activist, made public speeches in support of Mousavi during the election campaign and in the post-election rallies.
During heated television debates in the run-up to the vote, President Mahmoud Ahmadinejad had accused Rafsanjani's family of corruption.
Rafsanjani lost to Ahmadinejad in the 2005 presidential poll. However he remains a powerful figure as head of the top political arbitration body, the Expediency Council, and he Assembly of Experts, the 86-member body which selects the supreme leader and supervises his activities.
