The Brazilian National Foundation of Indians (Funai), a state organisation, said on Tuesday that the group had been located in the Javari river valley by its ethnologists, as they flew over the area in April.
Earlier, satellite images had shown three clearings in the rainforest that held four large huts in which the indigenous people live.
Experts also found areas devoted to growing maize, banana and possibly peanuts, Patricio Amorim, Funai's representative in the Javari valley, told Brazilian news agency Estado. Both these croplands and the huts "are new" and are believed to have been in use "for at most one year".
The finding highlighted the Javari valley's position as the holder of "the greatest concentration of isolated groups in Amazonia and in the world", Amorim said.
He said the physical and cultural integrity of these groups is under threat from non-indigenous people in the area who are active in illegal hunting and fishing, mining and farming, as well as from religious missionaries and drug gangs.