The seminar, entitled "Energy Reform for National Reconciliation," was organised by the Ministry of Energy. It will take place at the Army Club on Vibhavadi Rangsit Road between 9am-2pm, starting just an hour after the eight are released.
The source said military decided not to press charges against the activists after "attitude adjustment" talks were held and the group pledged not to repeat their Sunday energy-reform march on Bangkok's streets.
The former yellow shirt leader, who was recently released from a Cambodian prison, and the other advocates were whisked away by Metropolitan Police Bureau officers shortly after beginning their procession on Phahon Yothin road from Victory Monument to support an earlier, military-halted march in the South by energy-reform advocates.
They were arrested for defying the martial law's ban on public gatherings of more than five people.
NCPO spokesman Col Winthai Suvaree said Prime Minister Prayuth Chan-ocha wanted everyone to attend the seminar, especially those with differing views and information on energy issues, including Mr Veera and his colleagues.
Among the eight activists arrested on Sunday were Boonyuen Siritham, ex-senator for Samut Songkram and Itboon Onwongsa, leader of Thai Energy Reform Watch.