The eight were detained by troops on Wednesday over Facebook comments criticizing the draft, which has been denounced by groups on both sides of Thailand's political divide ahead of the Aug. 7 referendum.
Police said the eight had been charged over comments critical of the junta and the constitution.
The charges follow arrests over the past week of anti-junta activists who have held gatherings around the Thai capital amid growing criticism of the draft charter.
Critics say the charter entrenches the military's political influence. Among other things, it proposes an unelected upper house Senate to include a handful of top military and police commanders.
The military seized power in a May 2014 coup. Thailand has been torn apart by more than a decade of on-off protests and political instability since the army ousted billionaire former prime minister Thaksin Shinawatra in 2006.