Brian Roach's lawyers told a bail hearing he would plead guilty to attempted extortion, but not to terror charges.
They also said the 64-year-old was no longer seeking bail.
Roach is accused of sending emails threatening to spread foot-and-mouth disease in the US and Britain unless the governments paid him four million dollars (£2.5 million).
Prosecutors have said police have not found evidence that Roach had the means to carry out his threats.
Roach, who owns an engineering firm outside Johannesburg and has business interests in Zimbabwe, is accused of saying in emails that he wanted the money to compensate white Zimbabwean farmers for land lost, and accusing the US and British governments of not doing enough to help the farmers.
About 4,000 white farmers have been forced from their farms since 2000 in what Zimbabwean President Robert Mugabe calls a campaign to put more land in the hands of impoverished blacks.
Many of the beneficiaries, though, have been senior politicians who are close to Mugabe.
South African investigators worked with US and British officials on the case, and arrested Roach on February 12 after a seven-month investigation.
Daily Express
