By Agence France-Presse
The Journal cited unnamed sources close to the matter as saying the department would look into Google practices related to web search and other businesses.
Justice department officials share antitrust oversight with the Federal Trade Commission, which conducted a wide-ranging investigation of its own into Alphabet-owned Google that ended in 2013 with no action taken.
Google did not immediately respond to a request for comment.
A new investigation would come as backlash grows against major tech companies that dominate key segments of the online economy.
Democratic presidential candidate Elizabeth Warren has argued that big firms such as Facebook, Google and Apple should be broken up through antitrust enforcement.
Alphabet's profit in the first three months of this year sagged under the weight of a hefty antitrust fine in the European Union.
Alphabet said profit in the first-quarter fell 29 percent to $6.7 billion on revenue that climbed 17 percent to $36.3 billion.
The earnings took a hit from a European Commission fine that amounted to $1.7 billion at the end of March, according to the quarterly update.
Google's lucrative advertising platform remained the largest revenue driver for Alphabet, delivering more than $30 billion in revenue, but costs rose sharply as well.
But Google continues to face pressure around the world from regulators, notably in Europe amid multiple investigations over alleged abuse of its dominance in internet search, advertising and its mobile system.
The latest fine imposed by Brussels cited Google's AdSense advertising service, saying it illegally restricted client websites from displaying messages from ad service rivals.
Google is separately working to satisfy EU regulators investigating its hugely popular Android devices following a $5 billion fine last year.
Google earlier this year said it would offer smartphone users five browsers and search engines as part of the company's effort to meet EU competition concerns.
Brussels accused Google of using the Android system's dominance of smartphones and tablets to promote the use of its own Google search engine and Chrome browser and shut out rivals.
In the United States, Google has been a target of President Donald Trump and his allies who have accused the search giant of "bias" and silencing conservative voices, claims denied by the Silicon Valley firm.