The jurors deliberated 7 hours, 46 minutes, beginning Thursday, before finding Brent Betterly, 25, Jared Chase, 29, and Brian Church, 22, innocent of the more serious charges.
The three were tried on state terrorism laws, not under federal statutes.
They were convicted of two counts of mob action and of possession of an incendiary device, the Chicago Tribune and Chicago Sun-Times reported, but cleared of the more serious terrorism charges.
The jurors sat through a nearly three-week trial before being handed the case following Thursday's closing arguments.
The trio were accused by prosecutors of assembling four Molotov cocktails with the intention of inflicting as much damage as possible at the NATO summit in May 2012.
"When your hatred boils over into plots of violence, you've crossed the line -- the line that protects us all," Assistant State's Attorney John Blakey said in his closing remarks.
The defendants' attorneys say their clients were merely boasting and never intended to make good on their rhetoric.
"To me it trivializes terrorism -- the most serious type of case," Church's attorney, Michael Deutsch, said of the state's case against the three men. "You think of al-Qaida or the people who blew up Oklahoma City. This is not a case of terrorism."
The defendants' next court date for post-trial motions and possible sentencing was set for Feb. 28.