Syria's State Security Court jailed two Syrians and a Jordanian for belonging to extremist Islamic groups.
The court sentenced Ali Ahmad al-Ajeel, one of the Syrians, to 12 years in jail after initially ordering him to be sentenced to death for belonging to the outlawed Muslim Brotherhood, the National Organization for Human Rights in Syria said in a statement.
The other Syrian, Nidhal al-Khalidi was sentenced to six years in prison after the court found him guilty of belonging to a radical Islamic group, NOHR said.
Ibraheem Mohammed al-Taher, of Jordan, was sentenced to 15 years in prison for belonging to the al-Qaida terror network, the human rights group said.
"We appeal to the Syrian authorities to enforce the articles ... of the international convention regarding the civil and political rights that bond the freedoms of expression, of gathering and belonging to assemblies. ... And we plea to abolish the state security court," the National Organization for Human Rights in Syria said the statement.
There was no immediate comment on the verdict from Syrian authorities, which do not usually comment on cases deemed political or matters of national security.
When Syrian President Bashar Assad succeeded his father in July 2000, he released hundreds of political prisoners detained during Hafez Assad's 30 year rule. But he soon clamped down on pro-democracy activists, indicating there were limits to the amount of opposition he was prepared to tolerate.