E! News reported the man, whose identity has not been released, was struck by a van after the driver lost consciousness due to an unspecified medical condition.
The stricken security guard was taken to a hospital, but died of his injuries. The E! report did not offer any details about the driver or his condition.
Production on the show was subsequently shut down while the accident was investigated.
"Everyone at the network, the studio and 'NCIS' is devastated by the news," said a joint statement from CBS Television Studios and CBS Entertainment issued to E! News. "Our hearts grieve for his family and friends for this tragic loss. We are, of course, cooperating with the local authorities in Santa Clarita to help determine what caused this terrible accident."