"The proceedings refer to the period during which (chairman) Hans Dieter Pötsch served as the group chief financial officer," VW said in a statement.
The announcement is a fresh blow to VW's efforts to move on from the worst crisis in its history, which erupted in September last year after the group admitted to installing software in 11 million diesel vehicles worldwide that could dupe emissions tests.
Prosecutors in the German city of Brunswick are already investigating former CEO Martin Winterkorn and another former board member for allegedly holding back information from investors in the days after the scandal erupted.
By law, listed companies are required to disclose information that could affect market prices immediately. VW said it would stand by Pötsch, who was named supervisory board chief a month after the scandal broke.
"Based on careful examination by internal and external legal experts, the company reaffirms its belief that the Volkswagen board of management duly fulfilled its disclosure obligation under German capital markets law," VW said.
"The company and Hans Dieter Pötsch will continue to give the inquiries by the public prosecutor's office their full support."
More than a year since the "dieselgate" scandal rocked the industry, VW continues to be mired in legal and financial woes.
In a rare spot of bright news, the group last month won approval for a massive $14.7-billion (€13-billion) settlement in the United States that includes compensation for nearly half a million owners of the polluting vehicles.
But the company still faces criminal allegations over the cheating in the US, as well as a string of other legal cases including myriad lawsuits in Europe.
VW says it has so far set aside €18 billion to pay for legal costs and the refits and buy-backs of affected vehicles, but experts believe the final bill will be far higher.