The Washington-based Council on American-Islamic Relations in its report blamed the trend on lingering animosity toward Muslims and a growing use of anti-Muslim rhetoric by some political, religious and media figures.
The council counted 1522 incidents in which Muslims reported their civil rights had been violated in 2004, a 49% increase over 2003. Another 141 incidents of confirmed or suspected bias crimes were committed against Muslims – a 52% rise.
Notable bias or discrimination cases cited in a council report to be published on Wednesday include the barring of singer Cat Stevans, now known as Yusuf Islam, and Islamic scholar Tariq Ramadan from entering the United States.
Some Muslim leaders were surprised by the report's findings.
Yaser El-Menshawy, chairman of New Jersey's council of mosques, said he and others thought the number of anti-Muslim incidents shortly after the September 11 attacks on the World Trade Centre and Pentagon reached a peak that would not be repeated.
"I thought we were through with the high point after 9/11," he said. "My gut feeling is it may be a combination of the war in Iraq and mounting casualties, and that we are getting better at collecting this kind of data."