Abdella Ahmad Tounisi of Aurora was taken into custody at O'Hare Airport on Friday.
Prosecutors say he was attempting to travel to Syria to join a jihadist militant group. He had a one-way ticket to Turkey when he was taken into custody, charged with providing material support to a foreign terrorist organization.
Abdella Tounisi father, Ahmad Tounisi says his 18-year-son is a kind kid who is in college and prays every day. Ahmad Tounisi says he does not believe a word of the federal complaint against his oldest child.
While Abdella Tounisi remains in jail, his father refuses to believe Abdella planned to join a terrorist group tied to al-Qaeda.
"This is the worst time of my life. My first born is in jail. I don't know if he has been fed," Ahmad Tounisi said. "The kid doesn't know the terrorist group. Never been there. Never got there. He doesn't know nothing about fighting."
According to the FBI's complaint, the teenager spent months online searching various terrorist websites.
In late March 2013, Tounisi allegedly made contact with someone he thought was a recruiter for a jihadist militant group that is responsible for hundreds of terrorist attacks.
Instead, Tounisi's alleged online contact turned out to be an undercover FBI agent.
Tounisi talked about his willingness to die for the cause in email exchanges, according to the FBI complaint.
Ahmad Tounisi is Jordanian and he says all of his children were born in America. He believes his son is being targeted because of his religious beliefs.
"If you are at a mosque daily prayer, it raised a red flag," he said.
What raised the FBI's red flag was Tounisi's close friendship with Adel Daoud.
Daoud was arrested in 2012 for trying to detonate a bomb outside a Chicago bar. While Tounisi was not involved in that, the FBI says his search for terrorist websites followed.
Former FBI agent and ABC7 Public Safety Expert Jody Weis says the internet has become a huge recruiting tool for terrorist groups.
"There are numerous websites," Weis said. "These kids can find it."
Amhad Tounisi says his son used the computer often for international news and YouTube videos. He said he was not aware of any terrorist group searches.
The FBI stresses that this arrest is not related to the bombings at the Boston Marathon.