Sentencing for one count of attempting to provide material support to a designated foreign terrorist organization was scheduled for June 19.
A plea deal with prosecutors calls for him to spend 16 to 19 years in prison.
Lepsky only answered basic yes and no questions during his court appearance.
While searching computers and digital evidence, officers found evidence of Lepsky's plan to build and detonate a bomb as part of his support for ISIS.
Lepsky also bragged on social media he meant to fight for ISIS and wouldn't mind being a martyr.
A 20-year-old New Jersey man admitted he planned to use a pressure cooker bomb in NY in support of ISIS and become a martyr for the terrorist organization if necessary, according to the Department of Justice.
A search of Lepesky's internet history revealed that he had been researching ISIS and extremest groups throughout the month of January 2017.
In another search Lepesky had read an article from an extremist magazine that contained step-by-step instructions for building a homemade bomb with a list of supplies to be used.
Matches and a timing device, ordered online, were found at the home, along with several books on jihad and suicide bombings.
Lepsky - who once insisted his name was Allah Abdel Rochman - initially was arrested for trying to kill the family's pet dog with a combat knife.
According to post online, Lepsky pledged allegiance to ISIS and was planning to travel to Syria, so that he could fight with his 'brothers'.