Mohammed Hamzah Khan, a US citizen, was arrested at O'Hare International Airport in Chicago on October 4 before he attempted to fly to Vienna, Austria, on his way to Turkey.
He was charged in a criminal complaint filed in US District Court with one count of attempting to provide material support to a foreign terrorist organisation.
"I don't believe that the evidence is going to show that it was his desire to provide material support to IS," attorney Tom Durkin said after a preliminary hearing here.
Investigators allege Khan was attempting to leave the country in order to eventually sneak into Syria and join the IS.
More From This Section
"While Khan was at the airport, law enforcement agents executed a search warrant at Khan's home," a FBI special agent was quoted as saying by the ABC News.
"During the search, agents recovered multiple handwritten documents that appeared to be drafted by Khan or other persons, and which expressed support for IS," the agent said.
Khan's parents are originally from India. Khan was born in Chicago, Durkin said.
The federal judge postponed a detention hearing of Khan yesterday amid concerns that prosecutors wanted to close the courtroom to the public and media.
The decision by US Magistrate Judge Susan Cox came after prosecutors and attorneys for Khan met privately in her chambers for about 40 minutes to discuss the unusual government request.