According to the BBC, Ms Ghavami was freed because of health problems and was staying with her parents in Tehran awaiting a decision by the Court of Appeal .
Ms Ghavami, 25, and the other women were arrested and allegedly beaten after attempting to watch Iran play Italy in a volleyball match.
Hundreds of thousands of people have signed a petition calling for her release and Ms Ghavami has staged hunger strikes against her detention.
Yesterday Iran's Sharq newspaper tweeted that she was released after paying bail amounting to $38,000 (£24,000).
Her brother, Iman Ghavami, told the BBC's Newshour that their parents - who are in Iran - had wanted to ask for a full medical check-up because Ms Ghavami had "intestinal problems".
Mr Ghavami told the BBC his sister had served five months of a one-year sentence and that the release "was quite unexpected but a welcome move".
"Everyone is happy - my parents and my sister. There are many possibilities, we're not really sure what's going to happen, but we hope for the best outcome.
"For the time being... it's her 26th birthday tomorrow morning, so I think they're going to celebrate for a day or so."