Keefer appeared in dozens of television series, including other early anthologies: Fireside Theatre, Armstrong Circle Theatre, The Philco Television Playhouse, the United States Steel Hour, Alcoa Presents: One Step Beyond, The DuPont Show with June Allyson, and Death Valley Days. In 1957, Keefer appeared as McNair in the episode "Ito of Attu" on ABC Navy Log. That same year, he appeared with David Janssen as the character Reagan in "Big Score" of the CBS series Richard Diamond, Private Detective. In 1958, he appeared as Ed Locke in the episode "Wild Green Yonder" of the syndicated crime drama State Trooper, starring Rod Cameron. In 1959, Keefer appeared as John Alastair in the episode "Death Is a Red Rose" of the Craig Stevens NBC crime drama Peter Gunn. Keefer performed in three episodes of CBS's anthology Alfred Hitchcock Presents: in the role of Dr. Elkins in "The Indestructible Mr. Weems" (1957), as Pete Williams in "The Percentage" (1958), and as a tax clerk in "The Kiss-Off" (1961). He also had small roles in some feature films, including Woody Allen's Sleeper. In 1966, he played the character Irving Christiansen in the movie The Russians Are Coming, the Russians Are Coming.