The woman has been accused of posting "un-Islamic" and "nude" images of herself on social media - breaking the Islamic Republic's strict rules on 'revealing' clothing.
The woman has not been named but may be Shirin Nobahari, a bodybuilding fitness fan who has more than 68,000 followers on her Instagram account where she posts pictures and videos of her hard-earned physique.
Iranian authorities reportedly warned the woman arrested about selfies she was posting after taking part in an international competition last September.
"One of the female bodybuilders who recently published nude photographs on social networks has been arrested," the Iranian Judiciary confirmed.
She has been detained in prison because she was unable to post bail of two million rials ($60,000), according to the Mizanonline news agency.
After the Iranian Revolution in 1979, women by law were required to cover their heads in public spaces.
The ruling still stands today and is enforced by Iran's "morality police", Gasht-e Ershad, whose job is to enforce the "correct" Islamic code of conduct and dress.
While sportswomen in Iran are permitted to compete internationally, they are compelled to adhere to a strict Islamic dress code at all times.
According to these rules, "nude" can refer to a woman revealing any part of her body expected to be covered in public, for example if she is not wearing a veil.
Female swimmers have to wear full bodysuits and headscarves and women footballers and athletes have to wear tracksuits and long sleeves.
There have also been incidents where female sports fans were arrested for watching male sports events.
And earlier this year, Iran caused outrage after demanding international chess players have to wear a hijab while competing in a tournament that Tehran is hosting.