The friend, Kazakh exchange student Azamat Tazhayakov, was found guilty of conspiracy to obstruct justice and obstruction of justice for going to suspected bomber Dzhokhar Tsarnaev's room three days after the April 15, 2013 attack and removing a backpack containing empty fireworks shells.
The jury found Tazhayakov not guilty of similar charges involving a laptop computer.
His mother broke down in tears when the verdict was read, while Tazhayakov, dressed in a dark suit and tie, sat quietly between his lawyers.
Prosecutors have said Tazhayakov, fellow Kazakh exchange student Dias Kadyrbayev and Robel Phillipos of Cambridge, Massachusetts, went to Tsarnaev's room at the University of Massachusetts at Dartmouth and removed evidence after realizing that their friend was depicted in photos the FBI released of the suspected bomber.
Tazhayakov could face up to 20 years in prison on the obstruction of justice count and up to five years on the conspiracy count. He will be sentenced on Oct. 16, U.S. District Judge Douglas Woodlock said.
Kadyrbayev is awaiting trial on the same charges later this year, while Phillipos faces the lesser charge of lying to investigators.