This is said to be the estranged couple's first reunion since their split earlier this year, reported Us magazine.
"Gomez touched down in the country's capital, Oslo, shortly before Bieber hit the stage. There's no word yet on why she's there -- but if it is to see her ex, this would not be the couple's first reunion since their split earlier this year," a source said.
Last month, Bieber, 19, was spotted at the "Spring Breakers" actress' home in Los Angeles before he headed to Munich for another tour stop.