No price has been disclosed, but the airport was valued in the region of Â£100m.
Current owners EISER are selling the airport, used by around 2.7m people annually, along with other UK assets, to a fellow investment company, 3i.
The airport has not commented on the sale, which is expected to be completed early next year.
The airport last changed hands in 2008 for Â£132m, when it was sold by Spanish construction firm Ferrovial.
Its operating profit in 2015 increased to Â£3.3m.
The airport's managers are believed to want the new owners to invest in facilities, improving the likes of car parking.
They are also awaiting a planning decision on whether a seats-for-sale restriction can be removed.
Under its current planning agreement, the number of departure seats it can sell in a year is capped at two million.
A deal has been agreed between two UK companies for the sale of George Best Belfast City Airport.