Berlusconi's trial has been suspended due to a law he passed which gave him immunity from prosecution.
But this was then ruled unconstitutional, meaning two pending trials against him could resume.
Mills was convicted of taking a bribe in February this year, receiving a four-and-a-half-year jail sentence, pending appeal.
The prime minister, in a separate court hearing, has also been accused by a former mobster of making a political deal with the Mafia in the 1990s.
Gaspare Spatuzza, a Mafia gangster-turned-witness told a court in Turin that his boss in the Italian criminal organisation claimed to praised Berlusconi in aiding the mob.
Spatuzza said Giuseppe Graviano had told him in 1994 that the Sicilian Mafia had "the country in their hands" thanks to the help they received and that "everyone was profiting including those who are in prison".
According to the witness, Graviano said he "got everything thanks to the reliability of these people," before giving the names of the premier
But Berlusconi has denounced press reports of his alleged links to the powerful criminal network as "the most unbelievable, vile attack" he had suffered in recent years.
His spokesman, Paolo Bonaiulti, said: "It is completely logical the Mafia would use its members to make statements against the prime minister of a government that has acted in a determined and concrete way against organised crime".
The case is part of an appeal by Marcello Dell'Utri, a Sicilian business and political associate of Berlusconi, who was linked to a bombing campaign in 1993.
Dell'Utri, a senator in Berlusconi's People of Freedom Party, is appealing against his conviction of association with the Mafia. He has been sentenced to nine years in prison.