It is the only league honor that recognizes a player's community service along with his play.
The winning player will have $20,000 donated to a charity in his name. The award will be announced at the Super Bowl.
The 32 teams each nominated a player. A panel, including NFL Commissioner Roger Goodell, pared the field to three.
Asomugha is a four-time Pro Bowl cornerback for the Raiders. His foundation works with Orphans and Widows in Need, which supports women and children in Nigeria and provides food, shelter, medicine, vocational training, literacy efforts and scholarships.
Idonije is in his seventh season with the NFC North champion Chicago Bears. His First Down Attendance Program serves more than 600 economically disadvantaged students in five schools in Chicago and Manitoba, Canada.
Williams is scheduled to be in the Persian Gulf visiting with U.S. service members during Super Bowl week. He made a $2 million donation to create the Madieu Williams Center for Global Health at the University of Maryland, where he attended college. The center will address public health issues in Prince George's County and Sierra Leone, where Williams was born.
The award is named for the longtime Chicago Bears running back, who died in 1999.