They were each ordered to pay $75 in fines and court costs, but Sheehan's lawyer said he plans to appeal the verdict.
"We weren't demonstrating," Sheehan told reporters after the trial.
All the defendants contended they were trying to deliver petitions to the White House calling for an end to the war in Iraq on Sept. 26, but found no one willing to accept them.
"Our petitions were rejected like every request I have made of the president has been rejected," Sheehan said.
Sheehan, 48, of Berkeley, Calif., has tried repeatedly to meet with President Bush since her 24-year-old son, Casey, was killed in Iraq last year. She spent several weeks near the president's Crawford, Texas, ranch this summer.
Sheehan also plans to revive her protest near Mr. Bush's Texas ranch during Thanksgiving week, despite new county ordinances banning roadside camping.
"I absolutely believe he has an obligation to meet with me," Sheehan said.
She could have faced a $500 fine or 6 months in jail, CBS News reported.
"I'm willing to accept the full penalty because I don't want to live free in a country where murderers are free to roam and wreak havoc on our country and I'm talking about our administration," Sheehan said.
The defendants were among 300 people arrested by U.S. Park Police after they spent more than an hour on the Pennsylvania Avenue sidewalk north of the Executive Mansion. While some sat on the sidewalk, others chanted and sang songs. They were taken into custody after refusing police orders to leave. Each demonstrator carried a board bearing the name of a U.S. soldier killed in Iraq.
The arrests outside the White House concluded a weekend of protests that drew over 100,000 anti-war activists, and a smaller group of counter-protesters. It was the largest anti-war demonstration since the Vietnam War.
"The actions they were taking were designed to attract attention," said U.S. District Magistrate Judge Alan Kay.
A federal regulation prohibits demonstrations without a required permit outside the White House by groups larger than 25 people.
"They were consciously violating the law for publicizing their case," Kay said.
Sheehan said she plans to take her peace activist message to Europe next month with stops in London and Madrid.