The arrest comes after Russia banned the Jehovah's Witnesses and seized the organisation's property earlier this year because of alleged extremism.
Russian security forces have raided a Jehovah's Witnesses service and arrested a Danish citizen in the latest move against the Christian group since Moscow banned it as an "extremist organisation".
"Armed officers from the FSB" detained some 50 worshippers during a service Thursday in the town of Oryol, some 350 kilometres (220 miles) south of Moscow, a senior Jehovah's Witnesses official, Yaroslav Sivulsky, told AFP Monday.
Dennis Christensen of Denmark was then arraigned before a judge on Friday and arrested on charges of "participating in extremist activities," Sivulsky said.
The other worshippers were released without charge, he said.
The raid and arrest came after Russia's Supreme Court banned the Jehovah's Witnesses in April over alleged extremism and seized the organisation's property in the country.
The ruling sparked fears of a crackdown on religious freedom in Russia, where there are an estimated 175,000 Jehovah's Witnesses.
"This is the first time that a Jehovah's Witness has been jailed since the Soviet Union," Sivulsky said.
Members of the group - a Christian evangelical movement that was born in the United States in the 19th century - consider modern churches to have deviated from the Bible's true teachings.
They reject modern evolutionary theory and refuse blood transfusions.
The powerful Russian Orthodox Church spoke out against the group ahead of the Supreme Court ruling, with one church official branding it a "destructive sect".