Officials told the Los Angeles Times the actor and reality television personality was issued a citation for allegedly attempting to bring a "prohibited item" on board an American Airlines flight Thursday morning.
The grenade, which contained no fuse or powder, was allegedly in Knoxville's carry-on bag and was detected by an airport screener, the newspaper said.
The Los Angeles Police Department reportedly is investigating the incident.
TMZ said Knoxville still made his flight, despite being briefly detained.
Knoxville's film credits include "Men in Black II" and "The Dukes of Hazzard."