Murtaja Qureiris was arrested at the age of 13 for taking part in protests against the government and has been detained ever since, according to Amnesty.
Qureiris, now 18, faces possible execution for a series of offenses, some of which date back to when he was 10 years old, the rights group reported.
Saudi Arabia's public prosecution sought the death penalty for Qureiris last August for offences that include "participating in anti-government protests, attending the funeral of his brother Ali Qureiris who was killed in a protest in 2011, joining a 'terrorist organisation', throwing Molotov cocktails at a police station, and firing at security forces", Amnesty said in a press release on Friday.
CNN published video footage showing Qureiris allegedly participating in bicycle protests in Saudi Arabia's eastern province in 2011 along with a group of other young boys.
Saudi border authorities detained Qureiris when he was traveling with his family to Bahrain in 2014.
Amnesty said following his arrest, Qureiris was locked up at a juvenile detention center in the eastern city of Dammam and denied access to a lawyer until his first court session in August 2018.
Upon his arrest, Qureiris "was held in solitary confinement for a month, and subjected to beatings and intimidation during his interrogation", according to Amnesty. "His interrogators promised to release him if he confessed to charges against him."
Saudi Arabia has yet to respond to the report and the call by Amnesty International.
The teenager is currently awaiting his next trial session but human rights groups fear for his life.
Commenting on the case, Lynn Maalouf, Amnesty International's Middle East research director, said, "It is appalling that Murtaja Qureiris is facing execution for offenses that include taking part in protests while he was just ten years old.
"The Saudi Arabian authorities have a chilling track record of using the death penalty as a weapon to crush political dissent and punish anti-government protesters - including children - from the country's persecuted Shiite minority.
"There should be no doubt that the Saudi Arabian authorities are ready to go to any length to crack down on dissent against their own citizens, including by resorting to the death penalty for men who were merely boys at the time of their arrest," Maalouf added, according to the official website of Amnesty.
In April, Saudi Arabia executed 37 people for what it said were "terrorism" related crimes, publicly pinning at least one of the bodies to a pole as a warning to others.
Human rights groups said at the time that nearly all of the accused - who were beheaded - were from Saudi Arabia's Shiite community.
The sentences were carried out in Riyadh, central Qassim province, and Eastern Province, home to the country's Shiite minority.
The oil-rich Persian Gulf state is ranked among the top five executioners in the world, and according to Amnesty International carried out the death sentences of 149 people last year.