Mohammed al-Otaibi, 49, fled to neighbouring Qatar in March after he faced charges in Saudi Arabia related to his human rights work and was referred to an anti-terrorism court, the Gulf Center for Human Rights said in a statement.
Otaibi was "forcibly deported to Saudi Arabia" at dawn Sunday while on his way to Norway, said the Gulf Center, which has offices in Copenhagen and Beirut.
"It's regrettable that Qatar chose to deport that person to Saudi Arabia," Norwegian foreign ministry spokeswoman Ane Haavardsdatter Lunde told AFP in an email statement late Monday.
"We are concerned by the situation and we will continue to monitor the developments for this person through a dialogue with relevant organisations and countries," she added.
Andreas Skjold-Lorange, a spokesman for the Norwegian justice ministry, confirmed "that a Saudi human rights activist who had received a travel permit to Norway as a (UN) quota refugee has been sent from Qatar to Saudi Arabia".
He and his wife -- who was not deported to Saudi Arabia -- were not seeking asylum in Norway but have been processed as United Nations refugees, the ministry said.
Qatari authorities also confirmed the deportation, but said it had taken place on "Wednesday May 24".
The official Qatar News Agency (QNA) said that the deportation had been confirmed by a foreign ministry source.
"The extradition was... based on legal procedures and regional and international agreements relating to the extradition of accused persons and criminals," the agency said.
First arrested in 2009, Otaibi in 2013 co-founded the Union for Human Rights in Riyadh.
Authorities ordered it shut after about one month, but he continued his work, issuing reports and giving television interviews, the Gulf Center said.
New York-based Human Rights Watch warned in April that Otaibi would be at risk of a long prison sentence and possible ill-treatment if forcibly returned to Saudi Arabia.
On a visit to the kingdom early this month, a United Nations special rapporteur, Ben Emmerson, strongly condemned Saudi Arabia for using counter-terrorism legislation and penal sanctions "against individuals peacefully exercising their rights to freedom of expression", religion, or association.
Saudi Arabia says that human rights are a matter of definition and "values" from one country should not be imposed.
It says the kingdom has made great strides in rights to education, healthcare and other areas.
READ ALSO: Saudi Arabia slams Norway on human rights