Alexandria security forces released late on Wednesday Egyptian activist Maheinour El-Masry and three others, including her lawyer Mohamed Ramadan, after several hours in custody, El-Masry's sister told Ahram Online.
Wafaa El-Masry said no charges were levied against her sister and added that National Security officers asked her questions about her political orientation and opion of current political events while she was held at Al-Raml police station.
Wafaa had told Ahram Online earlier that Maheinour was not taking part in any protests when she was arrested in the Abu Kir district in the city's north east.
Activists on social media had reported that police arrested tens of protestors in Alexandria who were commemorating the third anniversary of Mohamed Mahmoud Street clashes in 2011.
A number of political groups called for marches in memory of 47 protesters killed and 3,000 injured in November 2011 in a violent standoff between the interior ministry and Tahrir Square revolutionaries.
El-Masry was acquitted late September after being detained since May and serving a six-month jail term after an initial two-year sentence earlier this year was reduced by an Alexandria court in July.
She and eight other activists were convicted on charges of "illegal protesting" during the Khaled Said murder retrial in December 2013.
A law banning all non-sanctioned protests was passed by Egypt's interim government that same month, imposing stiff jail terms and fines for violators.
Maheinour briefly joined a hunger strike campaign calling for the protest law to be revoked. Critics and rights groups have deemed it too restrictive.
Some 34 were arrested in Cairo Wednesday amid commemorative protests.