Harrison Nkomo, his lawyer, said: "He was arrested for publishing falsehoods and for contempt of court for an opinion article he wrote in April."
The article accused Mugabe of destroying the Zimbabwean economy and his security forces of abuses.
Trudy Stevenson, one of his senior allies and a former MP, confirmed that Mutambara, was picked up at his home by police and taken to a police station.
The editor of The Standard
was arrested last month over the piece written by Mutambara.
Mutambara, who leads a breakaway Movement for Democratic Change (MDC) faction, recently pledged to support Morgan Tsvangirai, leader of the main MDC group, in the run-off poll against Mugabe.Food summit
The Zimbabwean president arrived in Rome on Sunday for a summit of the UN's Food and Agriculture Organisation.
However, Steven Smith said on Monday that it was not right for Mugabe to be at the summit.
|"... Robert Mugabe turning up to a conference dealing with food security or food issues is, in my view, frankly obscene"|
Steven Smith, Australia's foreign minister
"This is the person who has presided over the starvation of his people ... [He] has used food aid in a politically motivated way," he said.
"So Robert Mugabe turning up to a conference dealing with food security or food issues is, in my view, frankly obscene."
Gordon Brown, the British prime minister, also condemned Mugabe's presence.
"We think it's particularly unfortunate that he has decided to attend this meeting given what he has done in relation to contributing to difficulties on food supply in Zimbabwe," a spokesman said.