Naisa faces charges of "carrying out activities contrary to the socialist system of the state" and "opposing the objectives of the revolution", according to his defence lawyer on Sunday.
Arrested in early April, the 53-year-old is president of the Committee for Defending Freedoms and Human Rights (CDFHR).
He has been kept in solitary confinement in Sadnaya prison in Damascus despite serious health concerns.
In a statement sent to Aljazeera on Sunday, the CDFHR said their chief's life was in danger "because he is suffering from heart and kidney problems and suffered a stroke while in detention."
Reason for arrest?
CDFHR recently published an annual report on human rights violations in Syria and has led a campaign for the lifting of the state of emergency.
Naisa's group also reported on human rights violations against Syrian Kurds in March and April, and repeated its concerns for the fate of scores of Lebanese who have disappeared in Syria.
Meanwhile Amnesty International said there was no case against Naisa and that he "should be released immediately and all charges against him dropped".
"Amnesty considers him a prisoner of conscience, arrested solely because of his work in defence of human rights."
The rights watchdog added it had information the activist had suffered a stroke and had been taken to Tishrin Hopsital, thus clearly in no state to stand before the Supreme State Security Court (SSSC).
Lawyer Anwar Bunni said Naisa was to be questioned by prosecutors for a second time on Sunday.
Bunni, another human rights activist, said the court had refused him permission to defend his client against a possible 15-year sentence at an eventual trial.
"Amnesty considers him a prisoner of conscience, arrested solely because of his work in defence of human rights"
Amnesty International statement
Two of the activist's colleagues, Ahmad Khadhim and Hasan Watfi, are also being held incommunicado at unknown locations since their arrests on 15 March.
A lawyer himself, Naisa has already spent six years in prison from 1991.
Amnesty has called for the lifting of the state of emergency, in force for 41 years.
It has also described trials before the supreme security court were "grossly unfair".
"Its verdicts are not subject to appeal, and it is not bound by the rules of the code of criminal procedures. Defendants have restricted access to lawyers.
"Judges have been granted wide discretionary powers, and confessions allegedly extracted under duress or torture are accepted as evidence."