Harben made 29 appearances in the Eastern League a season ago with Double-A New Britain. He was 4-9 with a 3.96 ERA in 122 2/3 innings.
The Cubs acquired the 23-year-old from Minnesota last fall, upon which he made three starts in the Arizona Fall League before being shut down.
On Monday, Harben threw his first bullpen session since the surgery.
"I'm probably throwing at 75 percent, but everything feels good," he said.
If all goes well, Harben is scheduled to face hitters in live batting practice on July 26, and then upgrade to simulated games afterward. He would like to make an official appearance some time later this summer in the AZL.
"Hopefully in the middle of August, I might be able to get into some games," an optimistic Harben said. "I don't know if I'll have time to (move up) because I'll only be throwing fastball-changeup."
Pitchers who have undergone Tommy John Surgery in the Cubs' system do not throw breaking pitches until at least 10 months after the operation.
Harben features a sinking fastball, changeup and curveball in his arsenal.
"I felt great," he said of Monday's bullpen session. "It was probably the best I've felt throughout this whole process. The ball was coming out of my hand real nice. It felt awesome. I can't wait to get a hitter in there and hopefully get into a game this summer."