Sihasak Phuangketkeow, permanent secretary for foreign affairs and acting foreign minister, said the six persons included Charupong Ruangsuwan, interior minister in the former Yingluck Shinawatra government and former leader of the Pheu Thai Party, and Jakrapob Penkair, former prime minister's office minister under the Thaksin Shinawatra government.
They refuse to report to the NCPO as ordered and on June 24 they announced on the YouTube website their setting up the Organisation of Free Thais for Human Rights and Democracy (FT-HD) to fight against the NCPO.
Mr Charupong is secretary-general of the organisation and Mr Jakrapob is its executive secretary and spokesman.
Another person whose Thai passport was revoked was Ms Chatwadee Amornpat also known as Rose.
She lives in England and was charged with insulting the monarchy via YouTube.
Another activist who faces passport revocation is former actor Atthachai Anantamek, now a pro-Thaksin red shirt activist.
Mr Sihasak said Mr Jakrapob was in Hong Kong and Thailand did not have an extradition agreement with the country.
He said the Ministry of Foreign Affairs was seeking other ways to reach Mr Jakrapob.
NCPO secretary-general Gen Udomdej Sitabutr told relevant authorities to inform the public that the military court had evidence and other suspects' testimony to back its warrant for the arrest of Mr Jakrapob for being involved in the illegal use of war weapons.
Gen Udomdej ordered further explanation of the need for the NCPO and its operations through diplomatic channels.
The order responded to some foreign news reports implying alleged human rights violations by the NCPO.