The probe will examine the company's practices in search and other businesses, the Wall Street Journal reported this weekend, citing people familiar with the matter.
Earlier this year, Google was fined $1.7 billion by European regulators for antitrust violations in the online advertising market.
"Usually a couple of days story and then the bad day if the Justice Department says something and then you get a bottom. You might be able to wait a couple of days if Justice doesn't say anything. You might get a bottom. People are panicking. I like to buy panic rather than sell it," said Cramer.