Reports say riot police were involved in a tense stand-off with protesters, but later retreated.
Protesters rallied after Nasser Zefzafi was arrested on Monday charged with threatening national security.
Mr Zefzafi has organised months of protests against unemployment and corruption.
Morocco has been gripped by demonstration since the death of a fishmonger in Al-Hoceima in October.
According to AFP news agency, protesters chanting "We are all Zefzafi" filled streets in Al-Hoceima on Tuesday evening and riot police were deployed in a square to stop their advance.
A stand-off ensued but police eventually backed down without incident.
Marches have also taken place in Casablanca and in the capital, Rabat, AFP reports.
The mass protests were triggered last October by the death of fishmonger Mouhcine Fikri, who was crushed to death by a rubbish truck as he tried to rescue his stock that had been confiscated by the police.
Thousands of protesters took to the streets accusing the authorities of corruption, abuse and injustice.
His death drew parallels to that of a Tunisian fruit seller in 2010 which helped spark the Arab Spring uprisings.
Thousands of people have demonstrated in the northern Moroccan city of Al-Hoceima, demanding the release of a well-known activist.