The group have topped the Paddy Power odds list at 1/1 to scoop this year's prestigious award with their album An Awesome Wave.
Meanwhile, Richard Hawley's Standing At The Sky's Edge is second favourite at 4/1, followed by Jessie Ware's Devotion and Plan B's iLL Manors at 6/1.
Discussing their nomination, Alt-J's Gus Unger-Hamilton told Digital Spy: "It's incredible to be nominated. To be in there with 11 other great artists is just a really nice feeling.
"May the best artist win."
It was recently announced that this year's awards has launched a new digital initiative, asking fans to tweet as part of a 'Voice Your Support' campaign.
The Paddy Power Barclaycard Mercury Prize 2012 odds appear below:
1/1 Alt-J (An Awesome Wave)
4/1 Richard Hawley (Standing At The Sky's Edge)
6/1 Jessie Ware (Devotion)
6/1 Plan B (Ill Manors)
7/1 Django Django (Django Django)
14/1 The Maccabees (Given To The Wild)
14/1 Ben Howard (Every Kingdom)
16/1 Field Music (Plumb)
20/1 Lianne La Havas (Is Your Love Big Enough)
20/1 Michael Kiwanuka (Home Again)
25/1 Sam Lee (Ground Of Its Own)
33/1 Roller Trio (Roller Trio)
Who do you think will win this year's Mercury Prize? Vote in our poll below: