All three denied the charges and were freed today without having to post bail.
They were freed on the condition they submit detailed testimony to the lead investigator in the case, explaining circumstances around the study they wrote.
They have about two months to submit the report so the investigator can decide whether to go ahead with the case, said one the activists' lawyers, Preeda Nakphew from the Cross Cultural Foundation advocacy group.
Amnesty International has called on Thai authorities to drop the charges and instead investigate the allegations in the report.
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The report issued in February described acts of torture in the southern provinces as systematic and said that in spite of complaints and campaigns by victims and rights organizations, "the state has not taken any significant action to prevent and address torture."
Government spokesman Winthai Suvaree said in response to their report that there was no evidence to support the allegations.
She was taken to the province of Narathiwat, 800 kilometers (500 miles) south of Bangkok late yesterday night, where she denied the charges. She was let out on bail early today.
Naritsarawan Kaewnopparat posted photos last year of her uncle's body and information about the torture he endured. She was arrested at her workplace in Bangkok on charges of criminal defamation and violating the Computer Crime Act.
Military personnel are rarely prosecuted for human rights abuses or other crimes in Thailand, and the military government that seized power in May 2014 has clamped down on free speech.