The 42-year-old labour activist and candidate in the cancelled Feb 2 election was apprehended after she disembarked from a flight from Sweden.
Immigration Police asked her to sign a document conceding that she defied the 44th announcement of the NCPO summoning her to report to the military, but Ms Jittra refused to sign it.
She was taken to the Crime Suppression Division for formal charge procedures.
Ms Jittra, an advocate of bail rights for political prisoners including those on lese majeste charges, departed Thailand on April 24, a day after red-shirt poet Maineung Kor Kuntheera was murdered in Bangkok.
"I did not defy the NCPO's order at all. Upon learning I was summoned I reported on June 3 at the Thai embassy in Stockholm, where I have been holidaying with Swedish friends at their invitation," Ms Jittra said.
"I think the embassy is part of the Thai state and since I could not get back to Bangkok right away, that's the thing I could do."
Ms Jittra rose to prominence as a leader of the labour union at the factory operated by lingerie producer Triumph. She was fired from her job.
She endeared herself with the red-shirts when she put up a paper banner saying, "Only good at Talking" in a protest against the government of former prime minister Abhisit Vejjaijva.
At the Feb 2 polls, which were later voided by the Constitutional Court, Ms Jittra, a Suphanburi native, ran as a party-list MP for the Palang Prachatipatai (Democratic Force Party).
The party was a breakaway from the Pheu Thai Party, which supported the controversial blanket amnesty bill. Ms Jittra and many other red-shirt sympathisers disagreed with a blanket amnesty for all involved in the protests since 2006, because it would also include members of the security forces who shot and killed people during the crachdown on the April-May 2010 protests.
The NCPO's 44th announcement at 8.20pm on June 1 summoned Ms Jittra and others to report to them on June s. She said she reported to the Thai embassy in Stockholm on June 3.