The unnamed cyclist in Najafabad was detained for breaking Islamic law.
A young woman in Iran has been arrested for cycling without a hijab in the latest defiant protest against curbs on women's freedoms in the country.
The woman, who has not been named, was shown in video footage riding her bicycle slowly along a street in the city of Najafabad, with her hair uncovered and raising her right arm in the air.
The video was widely circulated on the internet on Tuesday and within hours the woman had been traced and detained, state media reported.
"A person who had recently violated norms and insulted the Islamic veil in this region has been arrested," the local governor, Mojataba Raei, was quoted as saying.
The state-run news agency, Irna, reported that the sight of the woman "riding her bike without a veil in the main square" and "in front of a big mosque" had provoked angry protests from residents and clerics in Najafabad.
Wearing a hijab that covers the hair and neck has been compulsory for all women in Iran since the 1979 Islamic revolution, which saw strict dress codes imposed.
In 2016, the country's Supreme Leader Ayatollah Ali Khamenei issued a fatwa banning women from cycling in public, claiming it "contravenes chastity" by attracting the attention of men.
Several Iranian women have since been arrested for cycling or challenging the mandatory wearing of the hijab. Masih Alinejad, an activist with more than 206,000 followers on Twitter, shared the latest video and footage of similar cycling protests.
Speaking of the Najfabad cyclist, she told The Telegraph: "She was peacefully riding her bicycle with a smile on her face, to enjoy freedom, but now she's in jail.
"Right now, many women are in prison because of similar protests against the forced [wearing of the] hijab.
"I call these women the 'Rosa Parks of Iran'," she added. "They are imprisoned right now just because of this peaceful civil disobedience. This is beyond sad in the 21st century."
Alinejad, 44, who is now based in New York, said that her own brother had been arrested in Iran and sentenced to eight years in prison "to punish me for the crime of leading this campaign".
"But I will only shut down the campaign if women of Iran stop fighting and sending me videos of their civil disobedience."