Under the ruling, Anton may only see his Russian mother, Rimma Salonen, in weekly supervised visits.
The child's mother had appealed a lower Finnish court's decision to award custody to the father. The divorced parents have been waging a custody war for several years. The highly publicised case has strained ties between Finland and Russia.
"This is already the 22nd decision in the case," said Paavo Salonen of the latest judgment.
The Anton case has drawn attention on both sides of the border since 2008 when Rimma Salonen kidnapped her son from Finland and took him to Russia. A year later Paavo Salonen brought the boy back to Finland in the boot of a Finnish diplomatic vehicle. The move prompted Russia to send an official diplomatic note to Finnish authorities.