Azamat Tazhayakov, who attended the University of Massachusetts Dartmouth with Tsarnaev, faces up to 20 years in prison. He is the first of three Tsarnaev friends to go on trial.
Tazhayakov buried his face in his hands during part of the verdict, while his mother cried.
Tsarnaev and his older brother, Tamerlan, who was killed in a confrontation with police, allegedly set off two bombs at the Marathon finish line on April 15, 2013. The blast killed three people and injured more than 260.
Prosecutors said that Tazhayakov and Dias Kadyrbayev, who shared an off-campus apartment, removed a laptop and a backpack that held fireworks, a thumb drive and other items from Tsarnaev's dorm room on April 18. Tazhayakov was acquitted of charges involving the laptop.
Another UMass friend, Robel Phillipos, who also went to high school with Tsarnaev, is charged with lying to investigators.
A major issue in the trial was whether Tazhayakov knew Tsarnaev was a suspect. The brothers had not been identified by name when he and his roommate went to Tsarnaev's room, but photos from security cameras had been released.
Prosecutors presented evidence that Tazhayakov had done Internet searches on the bombing and on his friend's name.
Defense lawyers called their client "clueless." They said he was simply following Kadyrbayev's lead.
A cab driver friend of the Tsarnaev brothers has also been charged with aiding them after they became suspects.