The board members wanted Mr Chokechai to concentrate on his previous position as vice-president in charge of commercial affairs to help the national carrier reverse its financial losses, said ACM Prajin.
The decision was the biggest change at the airline since the National Council for Peace and Order (NCPO) took over the country on May 22. THAI is among the state enterprises in which the coup-makers want to see improvements.
Mr Chokechai was named acting president in December after Sorajak Kasemsuwan resigned.
As vice-president, he is in charge of marketing and route planning for the airline. He had close links to former chairman Ampon Kittiampon, who pushed him to be the acting president. Mr Ampon resigned from the board on June 20.
A source at THAI said that ACM Sivakiat Chayema, a board member, would take over as acting president for three months from July 1 while the company searches for a new president.
THAI posted a net loss of 2.63 billion baht in the first quarter, compared with a profit of 8.29 billion baht in the same period a year earlier.
Mr Chokchai said earlier that like other carriers, THAI was hurt by the political standoff in the period, when inbound and outbound tourist numbers fell by 17% compared with the fourth quarter of 2013.
Chinese tourist arrivals saw the biggest decline at 27.1%, followed by Japanese (down 25.2%) and Koreans (down 12.9%). Arrivals from Asean fell by 27.2%.
As a result, the airline filled just 70.1% of its seats in the first quarter, down from 79.8% a year earlier.