Thailand's generals seized power last year partially justifying their takeover as a necessary move to curb endemic corruption among the kingdom's civilian politicians and protect the royal family.
But the construction by the military of a park in tribute to the monarchy has engulfed the army in graft accusations that have undermined those anti-corruption pledges.
Jatuporn Prompan and Nattawut Saikuar, two leaders of the "Red Shirt" movement loyal to the ousted civilian government, were seized by the military on their way to visit the Rajabhakti Park in the seaside resort town of Hua Hin.
But Thai TV showed the two men being led away by soldiers into a van before they could set out.
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"Military authorities took them (Nattawut and Jatuporn) as it seemed to the authorities that they might incite disorder," junta spokesman Colonel Winthai Suvaree told AFP by phone.
Winthai added that he did not know where they had been taken or how long they would be held.
Rajabhakti Park was supposed to be a tribute to Thailand's monarchy from its royalist military, boasting seven enormous bronze statues of famous Thai kings.
But it has been dogged by allegations in local media and among opposition groups that large bribes were demanded for various construction contracts.
The junta leadership, including Prime Minister General Prayut Chan-O-Cha, has insisted there was no graft, but the reports have kept coming, transfixing a country where dissent has become rare.
Under pressure, the defence ministry last week announced its own investigation, but eyebrows were raised when it emerged that the probe would be overseen by Prayut's brother, who is also a general.
A string of senior police and military officers have been accused of falsely claiming connections to the palace to demand bribes and charged with lese majeste.
Two arrested suspects have since died in military custody and were quickly cremated.