The duo signed two-year deals to remain at the club until the end of 2023.
Mahony played 10 games in 2020, after debuting in Round 4 against Hawthorn, while Comben has yet to make his debut since his selection with pick 31 in the 2019 draft.
North Melbourne General Manager Brady Rawlings told North Melbourne media that the club is excited by the two youngsters.
“Jack had a really impressive debut year and showed he has what it takes at AFL. He was improving game-by-game which is all you can ask from a first-year player,” Rawlings told the club website.
“Charlie is yet to debut but we see him being an important part of our future. He has a strong, athletic build and we see him as a key part of our forward line going forward.
“We’re excited about what we’re building here at Arden St and are looking forward to further developing our next crop of talent.”