The identities of most of those brought into custody were not clear.
Reports, however, claim the estranged wife of the truck driver responsible, Mohamed Lahouaiej Bouhlel, had been taken away by police on Friday.
Islamic State have claimed Bouhlel was ‘a soldier’ of the group.
Meanwhile, a makeshift memorial of bouquets, candles and messages has been set up near one end of the famous Promenade des Anglais where the tragedy occurred.
France is observing three days of national mourning in honour to the victims.