TV bosses at Fox, who commission the show, are currently deciding whether to renew its contract after Kiefer and co are done filming the upcoming season.
"It's going to come down to a business decision," said the network's head of programming.
"It's not an inexpensive show on the network books and we also want to finish strong. This is not a show we want to prop up."
Kiefer, who has been talking about making a movie version of 24 for several years, beat House star Hugh Laurie in the list of high TV earners, revealed by TV Guide magazine.
In his role as the prickly medic, the British star earns $400,000 a show.
Other high earners included voice actors for The Simpsons, who earn $400,000 per episode, while Simon Cowell earns a cool $50 million per season of American idol.