Frank's diary -- in which she recorded how she and her family hid from the Nazis for two years during World War II before being discovered and taken to a concentration camp where she and most of her loved ones died -- is a literary classic.
Bieber, 19, recently visited the Anne Frank House, which has been turned into a museum dedicated to the 15-year-old author's memory.
"Truly inspiring to be able to come here. Anne was a great girl. Hopefully she would have been a belieber," he wrote in the museum's guestbook, prompting criticism from those who say the comment is inappropriate.
Bieber is to play three tour dates in Oslo, Norway, this week before playing at Parken Stadium in Copehhagen, Denmark, Saturday, The Hollywood Reporter said.