It means that children under the age of 16 should not have access to the artwork because it displays nudity.
"The FPB therefore presents to you that a classification rating of '16N' has been decided upon by the classification committee for the artwork by Brett Murray titled The Spear," it said in a statement.
"Any persons or entities wishing to publish and exhibit images and/or replicas of this specific artwork will in future have to put in place mechanisms to regulate access to this piece of art by members of the public below the age of 16."
The painting, which was vandalised last Tuesday, depicted President Jacob Zuma with his genitals exposed.
FPB chairperson Thoko Mpumlwana said the complainant had requested the board to give the painting a rating that no one under the age of 18 should have access to it. But the board decided to give it a "16" rating.
"It might also be worth noting that the said content has evoked a mixture of emotions from diverse sections of the populace and exhibitors would be advised to be cognisant of both the manifest and latent reactions that this specific work has drawn."