The FSB said it had arrested a 49-year-old soldier, whose name was not given.
Moscow routinely arrests people accused of working for Kyiv during its more than three-year offensive in Ukraine.
The FSB said in a statement it had "prevented a terrorist act planned by Ukrainian special services in a military unit of the Russian Defence Ministry".
The suspect faces up to 20 years in prison if convicted on those charges.
Russia regularly charges people who it says have collaborated with Ukraine with terror-related offences.
An FSB video, dated Wednesday, showed officers chasing the suspect in a park and making a violent arrest afterwards.
The agency also published photos of a purported stash with explosives.
Russia's Investigative Committee published an interrogation of the man, in which he said a Ukrainian secret service officer told him to wrap himself up with explosives and detonate near his unit.
He said a Ukrainian agent had promised his children would be evacuated to Western countries.
Russia has unleashed repression not seen since the Soviet era during its Ukraine campaign and soldiers refusing to fight have faced prison terms.
Kyiv rarely comments on alleged spy or sabotage activities inside Russia.
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