Earlier, a government official and a witness said the man had been arrested on suspicion of being the fifth member of the cell.
That cell was part of a bigger group that police have been looking for since March 11, when the suspected leader of a suicide squad detonated his explosives belt in an internet cafe to stop police arresting him, police sources said.
New blast was 'false alarm'
The government and security officials have denied earlier reports that a bomb had exploded in Fida, a working-class neighbourhood of Casablanca, earlier on Thursday.
Three suspected suicide bombers blew themselves up on Tuesday following a raid in which a fourth suspect was shot dead, police sources said.
Chakib Benmoussa, the Moroccan interior minister said late on Wednesday he suspected three to four members of the group might still be on the run.
An increase in extremist activity across the Maghreb in recent months has raised fears of a coordinated campaign by armed groups wanting to establish Islamic rule in the region.
On Wednesday, the Algeria-based al-Qaeda in the Islamic Maghreb claimed responsibility for bombs in the capital Algiers that killed at least 30 people.