Jurors declared Hamid Hayat guilty of providing "material support" to the enemy by training in Pakistan as a terrorist and of lying about it to FBI agents.
The verdict came just hours after a district court judge in Sacramento,
California dismissed jurors who couldn't agree whether Hayat's father, Umer, lied to the FBI about his son attending an Al-Qaeda camp in Pakistan.
Hamid Hayat, 23, trained with militants in Pakistan and planned an attack in the United States, Assistant US Attorney Laura Ferris argued at his trial.
He purportedly had the blessing and support of his father, an ice cream vendor from the California city of Lodi, according to prosecutors.
Umer Hayat, 48, who originally told FBI agents his son had nothing to do with terror camps, later confessed he paid for his son's flight to Pakistan and had family connections to the camp, according to the FBI.
The father paid his son a monthly allowance of US$100 while he was undergoing "jihadi training", court documents stated.
Ms Ferris portrayed the younger Hayat as an Islamic fundamentalist bent on carrying out jihad or "holy war", and promised to prove he intended to "commit jihad" in the United States.
Defence attorney Wazhma Mojaddidi countered that Hamid Hayat never attended a training camp. The father and son had separate juries in the district court.
Hamid Hayat was arrested by FBI agents in June of 2005 after he returned to California from an extended stay in Pakistan.
He initially denied attending terror-camp training in Pakistan, but confessed after flunking a lie-detector test, FBI agents reported.
He admitted attending an Al-Qaeda run "jihadist training camp" in Pakistan for approximately six months in 2003 and 2004, according to court documents.
Hayat told investigators he returned to California to await orders regarding where to strike, with potential targets including hospitals and large grocery stores.
Umer Hayat's attorney Johnny Griffin said he will fight to have his client released from custody while prosecutors consider whether to try him anew.
Prosecutors will consider the outcomes before deciding whether to pursue a retrial of the elder Hayat, said US Attorney McGregor Scott.
The decision should be made by a scheduled court status conference on May 5, according to Scott.