The three, who were among 11 arrested on Monday in Nice and the western city of Nantes, were remanded into custody yesterday, said the source. The other eight have been released.
The three, aged 24, 31 and 36, were charged in relation to a terrorist plot.
The arrests come five months after Tunisian extremist Mohamed Lahouaiej Bouhlel ploughed a 19-tonne truck into a crowd on the Nice seafront, further traumatising a country reeling from a series of jihadist attacks.
Six people have already been charged so far over alleged links to the 31-year-old killer but investigators have yet to prove that any of them knew what he was planning.
More From This Section
They include an Albanian couple, Artan Henaj and Enkeledja Zace, and a French-Tunisian national, 21-year-old Ramzi Arefa, suspected of providing a pistol to the killer while not necessarily knowing what he was planning.
The three men charged Friday are linked to varying degrees to these suspects.
The Islamic State group moved quickly after the attack to claim Bouhlel as one of its followers.
Nearly six months after the Nice attack, investigators are still trying to understand the killer's real motives.
"There is a combination of (Islamist) radicalisation, a fascination for extreme violence and a background of psychological problems," said a source close to the case.
The 23-year-old, arrested Tuesday in Mantes-la-Jolie west of Paris, was charged yesterday in connection with the alleged plot, foiled after the potentially deadly car was left near Paris's Notre Dame Cathedral on September 4.