Uncapped paceman Chadd Sayers and middle order batsman Nic Maddinson, who failed to perform in his first three tests, were dropped from the squad.
O'Keefe has been rested from the Sydney Sixers' Twenty20 match on Saturday and will vie with fellow left-armer Agar to bowl in a twin-spin attack with Nathan Lyon at the Sydney Cricket Ground test which starts on Tuesday.
O'Keefe teamed with Lyon against West Indies at the SCG in January and both took three wickets in the first innings of the rain-affected draw.
News that makes sense
Your trusted source for staying up-to-date with the world around you. Get free daily news updates and analysis, straight to your inbox.
The pair also bowled in tandem in the first test defeat in Sri Lanka in July before O'Keefe suffered a hamstring tear and was sidelined for the rest of the tour.
While the duo are likely to be reunited in Sydney, coach Darren Lehmann said two-test Agar also had a genuine claim as an all-rounder.
"He's made (Sheffield) Shield hundreds and obviously batted well in that test match at number 11," Lehmann told reporters, referring to Agar's impressive 98 on debut against England at Trent Bridge in the 2013 Ashes.
"He's certainly got the talent to be a batting all-rounder or a spinning all-rounder, either way."
Lyon came into the Melbourne test under pressure after a lean home summer but bowled his best spell on the fifth day against Pakistan, capturing three wickets as the tourists were dismissed for 163.
Steve Smith had declined to back Lyon as an automatic selection for Sydney but the skipper was effusive in his praise for the off-spinner after the win, as was Lehmann, who confirmed him Australia's "number one" slow bowler.
"I thought he was outstanding," Lehmann added.
"He bowled consistent line and length, which he was sort of up and down with in the previous few test matches, and really got through the middle order so I'm pleased for him."
(Editing by John O'Brien)
