These latest arrests came after two weeks of protests in the region to demand the release of Al-Hirak leaders who were detained a few weeks ago by authorities.
Moroccan police have detained four people in northern Morocco, an official and an activist said, as protests continued for a second week in the neglected Rif region.
"There have been three arrests in the past 24 hours," an official source said, without identifying those detained.
A local activist said six people had been brought in for questioning -- "three in the city of Al-Hoceima and three in nearby areas".
A leading protest figure was detained Saturday afternoon near his home in Al-Hoceima, a source close to the protesters and the official source said.
El Mortada Lamrachen was seen as a moderate voice in the grassroots Al-Hirak Al-Shaabi, or "Popular Movement".
The mainly Berber Rif region has been rocked by social unrest since the gruesome death of a fishmonger in Al-Hoceima last year.
Mouhcine Fikri, 31, was crushed to death in a rubbish truck in October as he tried to prevent the destruction of swordfish which had been confiscated because it was caught out of season.
Calls for justice snowballed into a wider social movement led by Al-Hirak demanding development, an end to corruption and jobs for the Rif.
Demonstrators have rallied nightly in Al-Hoceima and the nearby town of Imzouren since the arrest of Al-Hirak leader Nasser Zefzafi on May 29 and the subsequent arrests of dozens more.
Eighty-six people have been charged, including with "undermining internal security".
The Moroccan press has reported families have banded together to start a group to campaign for their release.
Protesters have gathered at night after breaking their fast as they mark the month of Ramadan during which Muslims refrain from eating and drinking from dawn till sunset.
Protesters gathered in Al-Hoceima late Saturday without incident, though numbers were lower than in previous days.
Around 500 people marched in protest in Imzouren, around 15 kilometres (nine miles) from Al-Hoceima.
"We are all Zefzafi", demonstrators shouted, demanding the detainees be freed, in a protest that was peaceful.
The previous night, protesters had clashed with security forces in Imzouren.
The Rif has long had a tense relationship with the central authorities in Rabat, and it was at the heart of the Arab Spring-inspired protests in Morocco in February 2011.
King Mohamed VI relinquished some of his near-absolute control through constitutional reforms following the 2011 protests.