Taoufiq Bouachrine, 49, was arrested during a police raid on his newspaper, Akhbar al-Yaoum, in Casablanca, Mounir Abou Al Maali told AFP.
He said around 20 policemen in civilian clothes entered the offices of the newspaper and searched it.
“They took pictures and confiscated the key,” to the office, he said.
Abou Al Maali said it was not immediately clear why Bouachrine was arrested.
The Arabic-language newspaper also said on its website that Bouachrine had been arrested, but it was also unable to say why.
It was not Bouachrine’s first run with the authorities.
In 2009, Bouachrine and Akhbar al-Yaoum cartoonist Khalid Gueddar were each given a four-year suspended jail sentence following two separate trials over a cartoon about a wedding which was deemed offensive to Morocco’s royal family.
The pair were also ordered to pay heavy fines and damages, while the paper was shut down.
Bouachrine has also faced lawsuits from government ministers who have accused him of defamation.
And in June 2010, Bouachrine was sentenced to six months for fraud relating to a property deal.
Media watchdog Reporters Without Borders (RSF) ranked Morocco 133rd out of 180 countries in its World Press Freedom Index last year.