The shares were traded at a price of 2.4 lei each, figures showed. The parties to the deal were not immediately known.
The bank's shares, part of the bourse's blue-chip BET index, was traded 1.35% lower at 2.2 lei by 1134 GMT on Monday.
The Bank of Cyprus Group said last week it has bought a 9.7% stake in Banca Transilvania for 58 million euro ($83 million).
(1 euro = 4.2137 Romanian lei)