They were among six people summoned on Friday night to turn themselves in at the Army Club in Bangkok between 10am and noon on Saturday.
Mr Somsak, who has written and commented frequently on the monarchy, also defied an earlier order to report to the coup-makers.
The four red-shirt movement leaders who did show up at the Army Club on Saturday morning were retired Lt Col Somjit Chuadet from Uttaradit, Somchai Mongkolsap from Mae Hong Son, Thanit Boonyanasineekasem from Chiang Rai, and Prasit Wuthinanchai, a former Pheu Thai MP for Chiang Mai .
The military court has issued warrants for the arrest of 27 people who have defied the NCPO's orders to report. They are liable to a jail term of up to two years and/or a fine of up to 40,000 baht.
Since the May 22 coup the NCPO has summoned more than 500 people, many of them political figures, red-shirt activists or businesspeople linked to the previous government.
Among the many academics the coup-makers have summoned, some were simply asked to offer their advice on the political situation, but others who hold anti-establishment views have been reluctant to report for fear of arrest.