In a statement issued on December 11, the bureau called on the Kazakh authorities to reopen the case against Vadim Kuramshin.
He was found guilty of extorting a bribe and sentenced to 12 years in prison on December 8.
Kuramshin, a defender of the rights of inmates in Kazakhstan's prisons, was first arrested in January and charged with fraud, extortion, and abuse of power.
In August, he was released after a court found him guilty of abusing his "responsibilities" as a human rights defender.
He was sentenced to one year of limited movement.
He was rearrested in October after prosecutors withdrew his initial sentence and sent his case for retrial.