Sources told the BBC that the young women were now in the custody of the Nigerian army.
They were brought by road convoy from a remote area to an army base in Banki near the Cameroon border.
The BBC's Stephanie Hegarty in Lagos says that many families in Chibok will be rejoicing at this latest news, but more than 100 of the girls taken have yet to be returned.
Christian pastor Enoch Mark, whose two daughters were among those kidnapped, told Agence France-Presse: "This is good news to us. We have been waiting for this day. We hope the remaining girls will soon be released." It was unclear whether his daughters had been freed.
A military source told the agency the freed girls would be flown to Borno's state capital of Maiduguri on Sunday.
After the Government Girls Secondary School in Chibok was raided in April 2014, more than 50 girls quickly escaped and Boko Haram then freed another 21 last October, after negotiations with the Red Cross.
The campaign for the return of the girls drew the support of then US First Lady Michelle Obama and many Hollywood stars.
Last month, President Muhammadu Buhari said the government remained "in constant touch through negotiations, through local intelligence to secure the release of the remaining girls and other abducted persons unharmed".