Mr Bennett, here with PM Tsvangirai, had only just returned to Zimbabwe
Charges of treason against Zimbabwean politician Roy Bennett have been dropped, and replaced with other allegations, his party says.
The new charge is conspiring to acquire arms with a view to disrupting essential services, the MDC said.
Mr Bennett, a deputy ministerial nominee, was arrested on Friday shortly before President Robert Mugabe swore in new ministers of the unity government.
His lawyer, Trust Maanda, said the treason case did not "hold water".
"The police must have realised that they had no leg to stand on," Mr Maanda told the AFP news agency.
But Mr Bennett remains in custody.
MDC supporters spent another night outside the police station in the eastern city of Mutare, where he is being held
"Bennett is currently being interviewed by the police. He is now appearing in court on Monday facing fresh charges," Mr Maanda said.
There was no confirmation from the police or justice officials that the charges had been changed.
Mr Bennett is treasurer of Prime Minister Morgan Tsvangirai's Movement for Democratic Change (MDC).
He had been picked by the party to be deputy agriculture minister in the new unity government.
Under a power-sharing deal agreed after months of talks following disputed elections, President Robert Mugabe's Zanu-PF is to have 15 posts and the two factions of the MDC 16 posts in the government.
The MDC has described Mr Bennett's detention as "scandalous" and "politically motivated", and called for him to be released unconditionally and unharmed.
A white farmer who lost his property under Mr Mugabe's land reform programme, Mr Bennett was imprisoned from October 2004 to June 2005.
The sentence was imposed by other MPs after he pushed a minister during an argument in parliament over land reform.
He recently returned to Zimbabwe after more than two years in South Africa, where he fled after police sought his arrest in connection with an alleged plot to kill Mr Mugabe.
The latest charges would appear to be linked to this alleged plot, reports the BBC's southern Africa correspondent, Peter Biles.
On Saturday Mr Tsvangirai said Mr Bennett's arrest was undermining the spirit of the power-sharing agreement.
Mr Bennett is one of more than 30 MDC supporters and other activists who have been detained over the past couple of months.