"Johannes Tomana, the deputy attorney-general is leading this plot," the party said in a statement, without giving details.
Tomana could not be reached for comment, but deputy information minister Bright Matonga dismissed the claims.
"We are now used to these malicious claims by the MDC. They are meant to make their Western sponsors happy and tarnish our government.
"There is nothing like that going on. The attorney-general’s office is independent of the government," said Matonga.
Fourteen MDC MPs on a police "wanted list" are either on remand or in police custody on charges linked to a spate of political violence after March elections that claimed mainly the lives of MDC supporters.
Five MDC MPs have been arrested since Monday, when the new 210-seat lower house of Parliament was sworn in.
Four are still being held on charges including attempted murder and rape – charges the MDC say mask a bid by President Robert Mugabe to overturn his party’s defeat in the March elections.
Morgan Tsvangirai’s MDC faction – the larger of two – took 100 seats in the election to Zanu-PF’s 99.
The plot claim comes a day after talks between the MDC and Zanu-PF on the formation of a government of national unity resumed in South Africa.
The last round ended in deadlock after Tsvangirai refused to sign a draft agreement that would have made him prime minister, but without the powers of a head of government.
State media accused Tsvangirai, whose party was emboldened by its victory in a vote on Monday for Parliament Speaker, of making fresh demands in the talks.
The Herald quoting unnamed sources as saying that Tsvangirai was demanding to co-chair cabinet with Mugabe and wanted to have the constitution changed to have three vice-presidents instead of two.
Nelson Chamisa, spokesperson for the MDC, refused to be drawn on The Herald story, saying the party was interested only in the democratisation of Zimbabwe and in turning around the battered economy.
Before the talks resumed Mugabe had been threatening to forge ahead with forming a government without the MDC – a move the MDC said would kill the talks.
On Friday, in a sign of a more conciliatory stance, the government lifted a nearly three-month ban on field work by aid agencies, whom it had accused of stumping for the MDC.
The lifting of the ban means the agencies can resume distributing food to around 2 million people in need. – dpa