Gas canisters, electric wiring and chemicals that could be used to make explosives were among items found in the flat near Villejuif, south of the French capital, the sources said.
One of the arrested pair, aged 36 and 47, is the owner of the flat, they said.
Paris police said a man who works at the apartment block had alerted police to "suspect items" in the flat.
Police found ingredients that can be used to produce the home-made explosive TATP, commonly used in attacks by ISIS, a source close to the case said.
Papers written in Arabic were also found.
The case is being handled by Paris anti-terror prosecutors, a judicial source said.
Since that large-scale attack and last year's Nice truck attack that killed 86, France has suffered a string of smaller assaults mainly targeting security forces.
In February, a man armed with a machete attacked four soldiers on patrol at Paris's Louvre Museum, while in April another terrorist shot and killed a policeman on the Champs Elysees, right before the presidential election.
In June, a radical Islamist rammed a car laden with weapons and gas canisters into a police van on the Champs-Elysees.
Last month, a man who was allegedly encouraged by ISIS, attacked a group of soldiers near the Eiffel Tower.