Justin Cathal Geever (born February 21, 1973), better known by his stage name Justin Sane, is an Irish-American musician and the lead vocalist, songwriter, and guitarist of anarcho-punk band Anti-Flag.

Having discovered punk rock and hardcore music at a young age, Justin has been writing songs since he was a teenager. After forming Anti-Flag at the age of 15 in 1988 with drummer Pat Thetic, the band went through several line-up changes and ultimately collapsed. After reforming in 1992 with bassist/second vocalist Andy Flag, the band released their first studio album, Die for the Government, in 1996.

Justin is known for his incredibly out-spoken left-wing views, and has written songs covering everything from alcoholism, to police brutality, to patriotism.