Bennett's arrest came hours after a unity government, comprising the MDC and President Robert Mugabe's Zanu-PF party, was sworn in.
Bennett and other deputy ministers are still waiting to be officially appointed.
The MDC had called the first charges "scandalous, vexatious and without basis in law" and "politically motivated".
Unity government doubts
Bennett had been living in exile in South Africa for two years after fleeing the country to escape charges of plotting to kill Mugabe, but returned last month.
He became treasurer of the MDC and was nominated by Morgan Tsvangirai, the MDC leader and now prime minister of Zimbabwe, for the post of deputy minister of agriculture.
Doubts have now been raised over the stability of the new unity government, which took several months to agree upon.
However, the MDC has not indicated yet if the arrest will trigger a crisis and endanger the coalition.
Foreign investors and western donors have said that funds will not reach Zimbabwe - which is undergoing an economic and humanitarian crisis - if there is no stability in the country.
Disputed elections prompted political violence in Zimbabwe in March.
Mugabe then won an uncontested presidential run-off in June, and a power-sharing deal was signed three months later.
However, disputes concerning the distribution of cabinet positions between the MDC and Zanu-PF prevented a unity government from being formed until last Friday.