Yonhap, citing unnamed sources, said the Korea Fair Trade Commission (KFTC) made the inspection last week and was probing whether Google forced smartphone makers using Android on their devices to not sell products using other operating systems.
Regulators began looking into the matter after the European Union brought charges against Google for anticompetitive behaviour earlier this year.
A person with direct knowledge of the matter told Reuters the KFTC conducted an on-site inspection at Google's South Korean headquarters but declined to elaborate further. Google and the KFTC declined to comment.
South Korea's antitrust regulator has investigated Google before. In 2013, the KFTC cleared Google of wrongdoing after a two-year investigation on whether the company hurt competition by forcing smartphone makers using Android to pre-load its search engine on the handsets.
© Thomson Reuters 2016