The three were in good health, according to a tribal chief involved in negotiating the trio's release, while a security official in southern Shabwa province said they would later Monday be transferred to the capital Sanaa.
"They are with me in Ataq (south Yemen), an hour after they were freed by Al-Qaeda," the tribal chief said.
News of their release was greeted by their Triangle Generation Humanitaire group, a French non-governmental organisation, as a "huge relief" after months of anxious waiting.
France thanked Oman, which borders Yemen to the east, for its "deciding assistance" in securing their freedom, without specifying what role it played.
Tribal sources said in July that the aid workers -- two men and a woman -- were seized by Al-Qaeda militants in the Hadramawt town of Seyun, 600 kilometres east of Sanaa.
Their car was found on the road some 20 kilometres from Shibam, a city known as the "Manhattan of the Desert" because of its spectacular high-rise mud-brick buildings, a Yemeni security official said at the time.
On July 27th, tribal sources said the kidnappers were from Al-Qaeda and were demanding a ransom of $12 million.
The three appeared in an online video in September, saying their abductors' demands had not been met.
France "warmly thanks the sultan of Oman and the Omani authorities for their deciding assistance, and all the people who contributed to this happy outcome", the French presidency said in a statement.
In September, Oman had paid the ransom for two US hikers held by Iran for more than two years.
Local Yemen sources said Monday that leaders of the Al-Awalaq tribe led negotiations with Fahd al-Qussa, a tribe member and a leader of Al-Qaeda in the Arabian Peninsula (AQAP), which kidnapped the three.
Triangle Generation Humanitaire said it was celebrating after hearing the three had been released.
"We have lived in anguish, waiting. Apparently they are in good health, that is another relief. We are now going to drink some champagne," the group's co-director Pierre Verbruggen told AFP.
He declined to name the three, saying only they were between the ages of 25 and 30.
They had worked in Yemen on an agricultural development programme.
The hostages had been held in Shabwa, the ancestral homeland of Anwar al-Awlaqi, the US-born Islamic cleric and Al-Qaeda leader who was killed in an air strike in September.
Foreigners have frequently been kidnapped in Yemen by tribes who use the tactic to pressure the authorities into making concessions.
More than 200 foreigners have been kidnapped in Yemen over the past 15 years, with almost all of them later freed unharmed.