Investigators apprehended an individual on Wednesday in the northern city of Meknes who had been "planning terrorist attacks in Morocco," according to a statement from the interior ministry.
The suspect had "acquired vast experience in the manufacture of remote-detonated explosives" and was "about to procure essential materials to make" a bomb, it added.
Last week three suspected extremists were arrested around Tangiers, in northern Morocco, reportedly in the process of preparing "extremely serious terrorist acts", the statement said.
Rabat says more than 150 "terrorist cells" have been uncovered since 2002, including dozens in the past three years with ties to jihadists in Iraq and Syria.
A study by the US-based Soufan Group said last December that at least 1,200 Moroccans had travelled to fight alongside IS in Iraq and Syria in the previous 18 months.