Moonves says Cote de Pablo was offered, in his words, "a lot of money" because the network didn't want to lose her from the crime drama. Moonves says the offer was then upped.
But he says the actress decided she didn't want to continue on the show.
He noted the social media outcry from de Pablo's disappointed fans, but asserted CBS did everything possible to keep her.
A representative for de Pablo didn't immediately respond to a request for comment.
"NCIS" stars Mark Harmon as head of a Navy criminal investigations division. It returns for its 11th season this fall.