The boy was reported to police on Sunday last week by the parents of the girl, writes broadcaster NRK.
The assault is reported to have taken place in Grenland in Telemark county on Friday last week and was initially reported by newspaper Varden.
“The boy is suspected of rape and for spreading material of a sexual nature involving children,” police attorney Torunn Fossli Sæthre told NRK.
Preliminary hearings were scheduled for Friday.
Police have found a video recording of the assault on the 14-year-old boy's smartphone. The same film – which clearly shows an assault but not the identity of the girl – has been found on the device of a second person, reports NRK.
“We don't know how many people it has been sent to, but take the fact this happened very seriously. This makes the assault and the crime much worse,” Fossli Sæthre told the broadcaster.
The accused teenager is currently being held in a youth detention facility in Telemark.
Norway's Child Welfare Services (Barnevernet) agency will be involved in the case, including any detention of the accused individual, given that he is under the minimum criminal age of 15.
“Police are now further investigating the case in order to find out what happened. What will then happen to the boy is the responsibility of Barnevernet. The accused is a child,” Fossli Sæthre told NRK.