The four men and two women, who did not have any travel documents, were apprehended at around midnight in Sindhupalchowk district Sunday, police said Monday.
The group was handed over to immigration authorities for investigation and necessary action, they said.
The arrests, the first reported ones in the new year, came after a leaked US embassy memo from New Delhi recorded an unnamed source as telling American officials that "Beijing has asked Kathmandu to step up patrols of Nepali border forces and make it more difficult for Tibetans to enter Nepal".
The source also said, according to the leaked cable: "The Chinese government rewards (Nepali forces) by providing financial incentives to officers who hand over Tibetans attempting to exit China."
WikiLeaks had published the memo in December 2010.In the past, following an agreement with the UN agency looking after refugees, Nepal used to hand over Tibetans to it for their passage to India, where they usually go to the seat of their exiled leader, the Dalai Lama, in Dharamsala.
However, following China's pressure, Nepal's governments first began to arrest and jail the refugees and on certain occasions, even handed them over to Chinese authorities, triggering international outcry.
China says there are no Tibetan refugees, only illegal migrants who should be given harsh punishment to stop the exodus.
Beijing has also implied that its relations with India would improve if New Delhi shuts down the Dalai Lama's office there.This year, Nepal's dependence on China has grown as it is regarding the communist republic as the second largest source of tourists to make its "Visit Nepal 2011" year a resounding success.
Nepal is hoping to attract one million foreign tourists and China, the second major source of tourists after India, is being wooed to send 100,000 visitors.