The 17-year-old boy pleaded guilty to planning a terrorist act between April and May this year.
He admitted the charge ahead of a committal hearing and prosecutors dropped two other charges.
Reports said that earlier hearings were told he prepared to make explosives after obtaining instructions online.
Police also told the court that radical Islamic propaganda was found during the raids.
The boy did not apply for bail. He has been remanded in custody and is set to appear in court again on Thursday.