Dressed in khaki prison uniforms, the 70 - all of whom are foreigners with the exception of one Zimbabwean - appeared at the special court, set up at a maximum security prison, wearing shackles on their legs and arms.
The state read out five charges against them, some of which attract a life term on conviction. They were not asked to enter their pleas.
These include two charges relating to conspiracy to possess and purchase "dangerous weapons," which can attract the life sentence; and violation of firearms laws, immigration regulations and civil aviation laws.
An earlier charge of "conspiring to "commit international terrorism," was not mentioned on Tuesday.
Magistrate Mishrod Guvamombe remanded the men - from South Africa, Angola, Namibia, the Democratic Republic of Congo, and only one from Zimbabwe - until 13 April.
"These sponsors have the capacity and the capability of launching an air and ground operation to rescue their cadres"
About 100 members of the public, including relatives of some of the accused, were allowed into the improvised courtroom in the Chikurubi maximum security prison on the outskirts of the Zimbabwean capital Harare.
The men, detained since 7 March, have been linked to 15 alleged coup plotters in oil-rich Equatorial Guinea who have been charged with trying to murder long-serving President Teodoro Obiang Nguema.
Sixty-seven of the detainees in Zimbabwe were aboard a Boeing 727 that was impounded at Harare International Airport, while three others were arrested when they went to meet the plane.
Zimbabwe military officials hold up
wire cutters found on plane
The suspects deny the charges and insist they were hired in South Africa to serve as security guards at a diamond mine in the Democratic Republic of Congo.
Harare has said the men landed in Zimbabwe to pick up an array of weapons including AK47s, rocket launchers, grenades and ammunition, allegedly for use in the coup.
On Monday, a high court judge, dismissed a plea from the defence lawyer for a public trial and ruled in favour of the Chikurubi prison where the men are detained following pleas from the state lawyers that the men be tried in prison because of concerns over public security.
Court papers filed by the state charged that the suspected mercenaries were "sponsored externally", and this posed real security risks.
"These sponsors have the capacity and the capability of launching an air and ground operation to rescue their cadres," the papers said.
The US-registered plane which
carried the 'mercenaries'
The state also argued on Monday that the Zimbabwe Prisons Service (ZPS) had no suitable transport to get the men to a public court, and that Chikurubi prison is officially designated as a place to hold court hearings.
Reading his judgement, Karwi said he had taken into consideration the need for a fair trial, and ordered that the proceedings take place in a large room at the prison big enough "to accommodate more than 100 people seated at any given time".
He also ordered that lawyers, friends and relatives of the detained men, as well as members of the press, be "given easy access to the venue".
"The state must comply with these orders," Karwi added.