Egyptian 2011 uprising leader arrested for insulting Sisi
The activist was also accused of spreading fake news, his wife Fatima told AP.
Harb's bail was set at 50,000 Egyptian pounds ($2,800). It has been paid but authorities have refused to release him, she said.
Harb's lawyer Doaa Moustafa said he is being held for 15 days pending investigation, and that he is also facing charges of joining an outlawed group. His case has been added to another investigation involving activist Amal Fathy and comedian Shady Abu Zaid, both currently in custody.
Egyptian authorites have carried out a sweeping crackdown on dissent since seizing power more than five years ago. Tens of thousands, mainly Islamists but also secularists and other dissident groups, have been arrested since. Harb was a leading figure in the 2011 uprising that toppled longtime strong Hosni Mubarak. He initially backed the 2013 ouster of the Islamist Mohammed Morsi, but became a critic of the military regime that followed.
The government has also banned protests that are not authorised by the Ministry of Interior. Hundreds of websites have also been blocked by authorities.On Friday, Egyptian police also detained activist Amal Fathy after she posted a video criticising the government's failure to address sexual harassment in the country.
Amnesty International called Fathy's arrest a "new low in Egypt's crackdown on freedom of expression".
Follow us on Twitter: @The_NewArab