The group were performing their encore at the Rogers Arena in Vancouver when the 53-year-old took a tumble.
A video posted online of the incident shows the guitarist appearing to misjudge the unconventional shape of the stage and stepping off the side.
He later posted a picture of his grazed arm on Instagram saying: "Didn't see the edge, I'm ok!"
U2 have just begun their Innocence + Experience tour, which will see them play some 70 dates across North America and Europe.
It is not the first stage fall the band has had the misfortune to experience - frontman Bono has taken a dive on several occasions.
He fell backwards off stage at a Miami concert in 2001 and slipped off a rainy stage in Washington DC in 1987 - dislocating his arm and requiring him to wear a sling for a dozen shows.
He also fell in 1983 during a gig in Germany after trying to climb a barricade.
Last November, Bono also underwent five hours of surgery after breaking his arm in six places and suffering a broken eye socket as a result of a "high-energy bicycle accident" in New York.
U2 guitarist The Edge has said he is fine after falling off stage during the opening night of the band's world tour.