Law enforcement personnel escorted Williams off a plane at Los Angeles International Airport Wednesday after Mexican officials arrested him Tuesday in the Caribbean town of Playa del Carmen, the Los Angeles Times reported.
Earlier this week, Walter Lee Williams, 64, was added to the FBI's 10 Most Wanted list.
Bill Lewis, FBI assistant director in charge in Los Angeles, said a Mexican citizen spotted Williams after seeing the fugitive's picture in a newspaper.
Williams "was actively writing and publishing" in Mexico and wasn't "living under an assumed name," Lewis said.
"We had an idea he may have fled to Mexico," Lewis said, adding that the location wasn't known until the witness contacted authorities.
The FBI said authorities have identified at least 10 of the alleged victims, who are 9- to 17 years old. Officials said many live in third-world countries.
A four-count federal indictment filed April 30 alleged crimes involving two 14-year-old boys Williams met online in 2010. He allegedly "engaged in sexual activity via Internet webcam sessions with the boys and expressed a desire to visit them in the Philippines to have sex," the FBI said in a statement.
Williams fled Los Angeles after he was questioned by FBI agents.
Williams taught anthropology, gender studies and history at USC, information on a university Web page said. The page since has been removed.
Williams is a Fulbright award winner who received the USC General Education Outstanding Teacher Award in 2006.