Cushnahan has been a prominent businessman in Northern Ireland over many decades, working in both the private and public sector.
The trial dates back to 2013 when he was an advisor to Nama, and there was the potential sale of its Northern Ireland loan book after the financial crash.
Cushnahan served as an adviser to Nama for three years.
It is alleged that between April and November 2013, he was providing assistance to an American firm called Pimco but did not tell Nama, even though, the prosecution say, he was under a legal duty to do so.
At the time, Pimco was interested in buying the Northern Ireland loan book from Nama. In the end, it was sold to another firm, Cerberus, in a deal worth more than £1bn.
It is alleged that by failing to disclose information to Nama, Cushnahan was in a position to make a gain for himself or someone else.
The trial at Belfast Crown Court is being held before a 12-member jury of nine men and three women.