Ales Byalyatski was sentenced in November to 4 1/2 years in prison for tax evasion.
The charges against him stemmed from his use of personal accounts in Lithuania and Poland to receive funding from international donors for rights activities in Belarus.
Byalyatski has pleaded not guilty, saying the case against him is politically motivated.
His friends have raised some $90,000 in January to pay the overdue taxes.
Byalyatski's wife, Natallya Pinchuk, says her husband has been ordered to pay an additional $17,500 as a fine for the tax payment's delay and a $876 state fee.
Pinchuk said the fines represented additional official pressure on her husband.