The men, between the ages of 27 and 67, were handed over on Friday at the truce village of Panmunjom, on the border between the two countries.
North Korea has returned six South Korean men to their homeland, South Korean officials say, in a rare move. Their names were not released and details surrounding their detention in the North remain unclear.
The two Koreas remain technically at war, as the 1950-53 conflict ended in an armistice and not a peace treaty. Pyongyang's Red Cross informed Seoul that the men would be handed back via Panmunjom on Thursday, a statement from South Korea's Unification Ministry said.
Officials said the group would be taken to South Korea's spy agency to face questions over their presence in North Korea.The South Korean government said that at first glance, the men were not on the list of those abducted by the North.
One possibility is that they may have crossed into North Korea illegally from China, the BBC's Lucy Williamson in Seoul says. Unofficial travel to North Korea by private citizens from South Korea is illegal,Pyongyang's state news agency announced the detention of several unnamed South Korean nationals in 2010 and there is speculation that they may be among those returned, our correspondent adds.
The move by North Korea is seen as a gesture of reconciliation following the cancellation of reunions for families split by the division of the Korean peninsula at the end of the Korean War which were planned for last month. Tensions between the two Koreas rose earlier this year, after North Korea's third nuclear test in February.