College baseball player Christopher Lane, 22, was shot in the back in the town of Duncan on Friday.
Police said one of the accused admitted Lane was killed for "the fun of it".
Chancey Luna, 16, and James Edwards, 15, were charged with first-degree murder; Michael Dewayne Jones, 17, has been named as accessory to the crime.
Lane, from Melbourne, had been visiting his girlfriend's family in Duncan. He was entering his final year at East Central University in the city of Ada, some 85 miles (137km) east of the town.
Because of the severity of their alleged crime, all three of the accused will be tried in adult court.
At Tuesday's hearing, Michael Dewayne Jones cried after he tried to speak about the incident but was cut short by the judge, who said the facts of the case would be determined at another hearing.
Bail for him was set at $1m (Â£640,000). The two younger accused were denied bail.
Duncan Police Chief Danny Ford told local television on Monday that one suspect had said Lane was killed at random.
"They saw Christopher go by, and one of them said, 'there's our target,'" Chief Ford said.
"The boy who has talked to us said, 'we were bored and didn't have anything to do, so we decided to kill somebody.'"
Mr Ford said they followed Lane in a car and shot him once in the back before driving off.
Witnesses rushed to help Lane after seeing him collapse on the road in Duncan, which has about 24,000 residents.
Family and friends in the US and Australia have been mourning him.
His American girlfriend, Sarah Harper, wept as she laid a cross by a memorial in Duncan at the spot where he was shot.
Melbourne's Herald Sun newspaper reported that roses and a baseball were placed on the home plate where Lane played baseball as a boy in a suburb of the city.
It was accompanied by a message that read: "A wonderful young man taken too soon. Why?"
The victim's father, Peter Lane, said there was no explanation for his son's death.
"It is heartless and to try to understand it is a short way to insanity," he told Australia's Sky News.
The mother of one of the accused was quoted by Australian broadcaster ABC News as saying that she could not believe her son was at fault.
"I get off work at three," she said. "It takes me five minutes to get home and he was there. That's what time they said it happened."
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