The copier and services company said the probe follows an earlier US Securities and Exchange Commission review into the company's financial reporting that led to a settlement with the agency in April.
Yesterday a spokesperson at the attorney's office would not confirm or deny that an investigation has been launched.
Xerox spokesman Christa Carone said Xerox has not yet heard directly from the US attorney's office, but expects any investigation to focus on possible criminal allegations related to past accounting practices.
The initial SEC probe into Xerox's accounting practices began in June 2000. In April, Xerox paid a civil penalty of $10m (£6.4m) and restated some of its financial results dating back to 1997 as part of the settlement with the SEC's Division of Enforcement.
In June, Xerox restated its income, reducing it by $1.4bn (£900m) for 1997 through 2001 after accounting irregularities.
Xerox is one of a growing list of companies in recent months to restate its financial results as a result of accounting irregularities.