Sayyid Imam al-Sharif, a former leader of the secretive Jihad group, and five other Egyptians were held in Yemen for more than two years before Sanaa handed them to Cairo in return for Yemeni opposition figures, Yasir al-Sirri said.
"The extraditions were made last month as part of a security settlement between the two countries," Sirri told Reuters by telephone from London, where he runs the Islamic Observation Centre rights watchdog.
He said he obtained his information from other Islamists and relatives of those extradited in Yemen and Egypt.
Sharif is a former leader of the Jihad group which bin Ladin's right-hand man Ayman al-Zawahri once headed. Jihad, under Zawahri, joined ranks with bin Ladin in 1998 in an alliance which they said would strike US and Jewish interests.
A Yemeni official said on Friday that Sanaa had handed over to Egypt six alleged Jihad members in the past two days.
But it was not clear if the six were the same mentioned by Sirri. Egyptian and Yemeni officials were not immediately available for comment.
Yemen is the ancestral home-
land of Usama bin Ladin
'No foreigners detained'
An official Yemeni website reported on Thursday that Yemen had captured a top Egyptian fighter, believed to be Sharif, in a security sweep last week. But the website later quoted a security source as saying there were no foreigners among those detained in the sweep.
Egyptian Islamists said the group handed over to Egypt by Yemen also included Othman al-Samman, who was sentenced to death in absentia by an Egyptian military court for belonging to al-Jama'a al-Islamiya.
Sirry said the six Egyptians were arrested in Yemen shortly after the 11 September, 2001, attacks on the United States, blamed on bin Ladin's al Qaeda.
Yemeni President Ali Abd Allah Salah said in Cairo last month that "the security file" between Yemen and Egypt had been settled. He did not elaborate.
Sharif, a surgeon in his early 50s, travelled to Afghanistan in the early 1980s to help Muslim fighters in the war against Soviet troops. A few years later, he joined the Kuwaiti Red Crescent in Peshawar, Pakistan.
He settled in Yemen after leaving Jihad in 1993 over his opposition to the group's confrontation with Egyptian authorities in the early 1990s.