Local media reported that the middle-aged woman and a man in his twenties had their face, head and legs bitten when the lion suddenly turned aggressive.
Another woman in her 20s was present when the incident took place, but was not injured.
The company's website shows that it is certified by the prefecture to raise 'dangerous animals,' and NHK reported the company had 15 lions under their care as of September last year.
But the police and the prefecture's health facility officials are investigating whether or not there were any abuse of animal rights or oversight in management.
Hideki Maruyama, chief of Inba Health and Welfare Center's hygiene department, said: 'We will direct the company accordingly if a problem comes to light based on (animal rights) law.'
Established in 1972, Shonan Animal Production is the largest animal actor agency in Japan.
The company has a total of 400 types of animals used for TV commercials and shows, according to Japanese media.
It relocated from the prefecture city of Togane to Narita in 2010 and owns approximately 10,000 square metres of land 1 kilometre northeast of Narita Airport.
It was not immediately available for comment.
The incident comes a month after a circus trainer was mauled by a lion during a live show in Egypt.
Trainer Islam Shaheen, 35, was filmed motioning at a lion with a stick as another lion climbed up a ladder during a performance in Alexandria.
At that moment, a third lion launched a savage attack on the trainer, rearing up and biting him in the neck as watching children screamed in terror.
Shaheen was rushed to Andalusian Salam hospital but died later from his injuries.
