Asked about reports according to which Belgium would sell one third of its 7.8% stake in the bank, the official said "we are indeed preparing an operation", declining to give further details.
BNP Paribas did not immediately reply to a request seeking comment.
The sale would mean Belgium will no longer hold the biggest stake in BNP Paribas.
(This story has been corrected to change "Belgian" to "Belgium" in headline and paragraph 1)
(Reporting by Charlotte Van Campenhout, Tassilo Hummel; Editing by Toby Chopra)
