Federal prosecutors say the men, who all lived in the Toledo area for a while, attended a Muslim convention in Cleveland during the summer of 2004 where they talked about training in explosives, guns and sniper tactics.
The men were there with a former US military man who worked undercover and helped foil the plot, prosecutors said.
Mohammad Zaki Amawi, Marwan Othman El-Hindi and Wassim I. Mazloum are accused of conspiring to kill or maim people outside the United States, including military personnel in Iraq. They have all pleaded not guilty.
All are US citizens except Mazloum, who came to the US legally from Lebanon while El-Hindi and Amawi are Jordanian-Americans.