Chief Justice Lawal Gumi said he had received information that someone was going around with money, claiming to know members of the court staff.
Nigerians have become notorious for dubious schemes promising vast wealth.
Nigeria's anti-graft agency says this trial shows it is fighting advance-fee frauds known as "419 scams".
The defence team assured the judge that nothing would be done to bring scandal to the administration of justice.
Five Nigerian suspects are charged with persuading an official at Banco Noroeste of Sao Paulo to part with a series of huge payments by pretending they were building a new airport in Nigeria, and promising him a cut of the contract.
"Under no condition should money be passed around in this case," the chief justice told the court.
"This situation should not surface under any condition whatever. Because of the nature of this case and the kind of personalities involved, the accused persons should be properly guided," he warned the defence team. (BBC)