According to the charges, the man, who used to be Mixa's altar server, phoned the bishop several times in the autumn of 2010 in his monastery in the southern German town of Fünfstetten.
According to a report in Die Welt newspaper, he told the bishop his child had leukemia, and that he also needed to borrow money for the treatment of his own illness. Mixa believed him and transferred approximately €4,800 to the 29-year-old's bank account. The money was never returned.
Mixa is to give evidence to a court in the Bavarian town of Ingolstadt on Thursday.
The man is said to have conned several other people, including two nuns. The verdict is expected on March 8.
Mixa was at the heart of a child abuse scandal in April 2010, when he resigned from his post as bishop of Augsburg following repeated accusations that he had hit institutionalized children during his tenure as priest in the small town of Schrobenhausen.