U.S. Attorney Preet Bharara in Manhattan is handling the investigation, which is said to be in its early stages, the Journal said, citing "people familiar with the case."
Bharara recently brought criminal charges against two former JPMorgan traders for understating losses from the bank's disastrous "London whale" derivatives trades last year.
It's not known if the new probe is criminal or civil. It was launched in the last few weeks as JPMorgan wrapped up a $410 million settlement with the Federal Energy Regulatory Commission over allegations of energy market manipulation in California and the Midwest. The bank did not admit wrongdoing in that case.
According to the report, the DOJ probe will look at some of the same issues involved in the FERC case.
A JPMorgan spokesman declined to comment on the report. A Justice Department spokeswoman in Washington had no immediate comment.
JPMorgan Chief Executive Officer Jamie Dimon has publicly vowed to resolve the company's regulatory issues.
— By CNBC.com with contributions by Reuters