Two Nigerians have been arrested for an alleged attempt to defraud the Bank of Ghana and an unnamed Accra businessman.
An official said some of the forgeries were convincing
The two allegedly sent the businessman what purported to be a letter from the Bank of Ghana, saying it had received a large transfer of funds for him.
But the letter said it was charging $7,000 a day for holding the funds.
A Ghanaian official said that some of the forged documents were quite convincing and could easily fool a lot of people.
In another incident, the two are accused of forging the signature of the central bank's deputy governor, authorising the release of $50m.
Ghanaian police say they believed both arrested men belonged to a gang running a series of what are known as "advance fee frauds".
They were arrested while have a meal in a restaurant and police say other members of the gang are on the run.
Nigeria's high commissioner to Ghana has reacted to the recent arrest of many Nigerians for fraud and robbery by stressing that the vast majority of his fellow countrymen are law-abiding.
The BBC's Kwaku Sakyi-Addo says there are tens of thousands of Nigerians living in Ghana.
Nigeria is rated the world's second most corrupt country and has become notorious for its fraudsters.
They send out letters and e-mails offering to deposit millions of dollars in bank accounts but instead they use the bank details to make withdrawals or demand a fee before transferring the funds.
Last year, Nigeria's anti-corruption commission said it had recovered some $200m from conmen in just eight months.
Nigerian President Olusegun Obasanjo has set up a special panel to fight economic crimes on the internet.