Ambassador Jacqueline Zwambila, aligned to opposition leader Morgan Tsvangirai, made the request for asylum ahead of the end of her posting next week.
She told Australian media that a July vote had been "stolen" by President Robert Mugabe's government and that she did not feel safe returning to Zimbabwe.
"Everyone is entitled to their opinion but her remarks are surprising because all the leaders of the MDC-T are here," said Home Affairs Minister Kembo Mohadi, referring to Tsvangirai's Movement for Democratic Change party.
"So, why does she feel threatened? What is so special about her? If she is threatened by anyone, she should tell us as we are responsible for security here as central government."
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Zwambila was appointed in 2009 after Zimbabwe's power-sharing government was set up between Tsvangirai as prime minister and Mugabe as president.
The shaky deal ended after elections in July this year, slammed as fraudulent by Tsvangirai, with the MDC losing its ministerial posts.
Zwambila said she was seeking a protection visa so she can stay on in Australia with her family once her diplomatic status expires. It was not immediately clear whether Canberra would approve her request.
"There is no way I feel safe being in Zimbabwe or going back to Zimbabwe," she said.
Zwambila voiced fears of indefinite detention if she went back, saying she had been threatened with arrest after a court found that she owed several hundred dollars to a tradesman, a charge she denied.
While in Australia, Zwambila was accused of exposing herself but was cleared by both a Zimbabwean government probe and a court in Australia, according to the MDC.