Lawyers for Roy Bennett had asked the court to drop the charges, saying another court had thrown out similar ones in a related case in 2006.
On Tuesday, the court formally charged senior MDC party official Roy Bennett for taking part in a plot involving terrorism and insurgency, just days after the party joined a unity cabinet.
He was also charged with banditry and violating the Immigration Act for leaving and returning to the country illegally, in a case that has raised doubts about the credibility of the new government.
The 52-year-old Movement for Democratic Change (MDC) politician now faces charges of possessing weapons for the purposes of insurgency and banditry, one of his lawyers, Trust Maanda, told Deutsche Presse-Agentur (DPA).
On Sunday, police had told his lawyers told he would be charged with raising finance for weapons, also for the purposes of insurgency and banditry – a lesser charge than treason which he faced at one point.
When he was first arrested on Friday at an airport outside Harare as he was preparing to leave for South Africa for the weekend, police said he faced charges of trying to leave the country illegally.
The charges against the MDC’s treasurer and fierce Mugabe critic relate to the discovery in 2006 of weapons near the eastern city of Mutare, where he is being held.
The State attempted to present the arms as part of a plot to topple Mugabe but the charges didn’t hold up in court. One person, a German-born arms trader, served time for illegal possession of weapons.
MDC leader, Prime Minister Morgan Tsvangirai, says the case is an attempt by hardliners within Mugabe’s Zanu-PF to derail the country’s fragile power-sharing government, whose cabinet members were due to meet for the first time on Tuesday.
The fact that police keep changing the charges shows the case against Bennett is weak and politically driven, critics say.
"This is purely a police case and we don’t understand where the political connotations are coming from." assistant police commissioner Wayne Bvudzijena retorted.
Bennett had been due to be sworn this week as deputy agriculture minister. On Monday, a magistrate gave permission for police to detain him without charge for a further 48 hours.
Bennett returned to Zimbabwe only last month after nearly three years in South Africa, where he was granted asylum in 2007.
Police are also holding more than 30 other MDC members and human-rights activists, mainly on charges of conspiring to topple Mugabe or of banditry.