The 19, led by United Front for Democracy against Dictatorship chairman Jatuporn Prompan, organised a Bangkok press conference in June to open the anti-fraud centres nationwide.
The authorities summoned them to face charges of violating NCPO order No 7 but they refused to meet police for over one month.
Dozens of supporters came at the CSD to show their supports to the red-shirt leaders amid tightening security.
After being charged, the 19 will be tried in the military court.
A lawyer of the 19 said they would deny the allegation.