The party led by radical writer Eduard Limonov has been banned in Russia and branded an extremist organization by the authorities.
"The incident took place at around 11:45 a.m. Moscow time (07:45 GMT), when a group of young people imitating a wedding procession tried to enter Red Square and hold an unsanctioned rally," the spokesman told RIA Novosti.
"The detainees say they are members of the banned National Bolshevik Party. Several placards and NBP symbols have been confiscated. A rubber-bullet pistol was seized from one of them."
The activists resisted arrest, and one of them let off a pepper spray in the face of a police officer, the spokesman said. They could face criminal charges.
On Tuesday Limonov, who has a strong youth following, said he would appeal to the European Court of Human Rights in Strasbourg over the Russian Supreme Court's refusal to lift the ban on his party.
The NBP has pursued 'direct action' tactics by publicly attacking people they considered symbols of President Putin's regime or its allies.
Group members are known to have thrown mayonnaise and tomatoes at prominent public figures, including ex-Prime Minister Mikhail Kasyanov, former NATO Secretary Lord George Robertson, Russian film director Nikita Mikhalkov. Activists have also staged protests by breaking into government offices in Moscow.
For such actions, which the radical group dubs "velvet terror," many of its activists were arrested and sentenced to prison terms.
Since founding the group in 1994, Limonov, 65, dropped his anti-capitalism rhetoric while preserving his nationalist message. In recent years, he has sided with the liberal opposition in Russia, which has been desperate to strengthen its ranks.
