Cushnahan, from Alexandra Gate, Holywood, County Down, has been a prominent businessman in Northern Ireland over many years, working in both the private and public sector.
The case dates back to 2013, when Cushnahan was an adviser to Nama, and there was the potential sale of its Northern Ireland loan book after the financial crash.
It was alleged that between April and November that year, he provided assistance to an American firm called Pimco but did not tell Nama, even though, the prosecution said, 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 was alleged that by failing to disclose information to Nama, Cushnahan was in a position to make a gain for himself or someone else.
It was claimed that he stood to gain about £5m in a success fee if the deal went through.
The charge was denied.