Infrastructure company Abertis, which is based in Barcelona, said it is reviewing its 29-strong airport division.
A company spokesperson said: "We have started a process of reviewing our airport division, including the possibility of a future sale of the division."
Abertis acquired Belfast International through its company TBI in 1996.
Around 12 million passengers use the airport every year.
The spokesman for Abertis said selling the Northern Irish airport was a "possibility, but it has not happened yet".
The company - which also owns Cardiff Airport, operates Luton Airport under a long-term contract, and has further airports in Mexico, America and Sweden - said it appointed Citi and AZ Capital to look into the future of the division.
On Sunday night, a Belfast International Airport spokeswoman told UTV: "The airport's owners Abertis are currently undertaking a strategic review of their airport division. The airport is not up for sale."