Mukhtar al-Bakri, 23, is the first of the so-called "Lackawanna Six" - all US citizens of Yemeni descent - to be incarcerated.
The six were arrested more than a year ago and all eventually pleaded guilty to the charge of providing material support to al-Qaida.
They also agreed to cooperate with US authorities, and to provide information on their stint in an al-Qaida training camp in Afghanistan.
The group attended the camp near Kandahar in the spring of 2001.
As well as receiving weapons training, they heard an address by al-Qaida leader Usama bin Ladin who, according to testimony from the six, announced that 50 men were on "a mission to attack America".
Jabir al-Banah is wanted by the
Federal investigators had rounded up the six suspects in Lackawanna near Buffalo in September 2002 after detecting a new tone in their telephone and e-mail communications.
The group was apparently using new code words and phrases that suggested a possible "terrorist" attack, the investigators said.
However, defence lawyers had argued there was no evidence any of the defendants posed a risk to the community.
Sentencing of the five other members of the cell will take place over the next two weeks.
A seventh man, Jabir al-Banah, charged in May with membership of the group, is still at large and believed to be abroad.