John T. Booker Jr., 20, appeared in US District Court in Kansas City, Kansas, wearing an orange jumpsuit and his legs in shackles, The Topeka Capital-Journal reported. He politely responded to US Magistrate Judge James P. O'Hara's questions as he entered his plea.
Booker was arrested April 10 while trying to arm what he thought was a 1,000-pound (450-kilogram) bomb inside a van near the Army post an hour west of Topeka, according to court documents.
Prosecutors allege Booker told an FBI informant he wanted to kill Americans and engage in violent jihad on behalf of IS, and that he believed such an attack was justified because the Quran "says to kill your enemies wherever they are," according to a criminal complaint.
A Muslim cleric who said he was counseling the suspect at the request of the FBI told The Associated Press that Booker suffers from bipolar disorder and had been acting strangely days prior to his arrest.
A second man, who was charged with knowing about Booker's plan but failing to report him to authorities, was ordered released into his parents' custody last week.