About 40 people are now in custody on similar charges relating to the alleged insurrection plot.
On Wednesday, Harare magistrate Olivia Mariga ruled that one of those detained in connection with the alleged plot, human rights activist Jestina Mukoko, had to remain in custody. She was abducted by alleged intelligence agents early last month and her fate remained unknown for three weeks.
Mukoko and others have claimed police tortured them and High Court judges have twice ordered their release to be medically examined or treated.
But authorities have defied the orders on grounds that the State is appealing against them.
All are being held for the alleged insurrection plot though no charges have been laid against them.
Mariga ordered that Mukoko should remain in custody pending determination of the matters in the High Court. Meanwhile, police sources said they had arrested "three white adult males" who run an adventure company. Sources said they would be charged with training bandits to topple Mugabe.
The three run an outdoor training camp called Kudu Creek in Ruwa, 30km from Harare.
It trains Boy Scouts, tourists and others in outdoor living and is well known in Ruwa.
A police officer said in Harare that the three are likely to face terrorism charges. "Police arrested three white adults after getting a tip-off that they are training bandits …
"The three were former Selous Scouts under Ian Smith’s Rhodesia and investigations are in progress."
But police said they had not yet laid charges against them.
Frightened residents of the area around the training camp said heavily armed soldiers, police and intelligence officers first raided the camp last Friday and took away the three for questioning. But they were released the same day before being re-arrested yesterday morning.
A Ruwa resident said: "The guys who were arrested have been conducting training for Boy Scouts in outdoor living for years and it is not even a secret.
"They advertise their facility in the newspapers and everybody knows about them.
"We have top government officials who live in the same area and they are aware of what these guys are doing, but we are surprised to hear that they are training bandits.
"Even the soldiers and police who raided the area last Friday were laughing it off saying they had been taken for a ride by their informer.
"What shocks us is that one of them deals with government by supplying tractors," said a neighbour.