Christopher Ahn is expected to appear before Central District of California Magistrate Judge Jean Rosenbluth at 2 p.m. (2100 GMT), according to a court calendar posted online.
It is unclear what charges Ahn faces as the case has been sealed. A source familiar with the case told Reuters that the defense requested the case be sealed while prosecutors were willing to allow to have case records unsealed.
Ahn was arrested on Thursday and appeared on Friday in federal court, according to a law enforcement official and a source close to the group.
A US Justice Department spokeswoman declined to comment on the case last week.
Ahn was part of a group of at least 10 people accused of storming into the North Korean embassy in Madrid, where they restrained, beat up some personnel and held them hostage for hours before fleeing on Feb. 22, according to a Spanish court.
A judicial source in Madrid said last month that the group was trying to persuade a North Korean official there to defect, adding a Spanish judge wants the suspects extradited from United States.
Spanish investigators said the intruders, self-professed members of a group that calls itself Cheollima Civil Defense seeking the overthrow of North Korean leader Kim Jong Un, removed computers and hard drives from the embassy before fleeing to the United States where they handed over the material to the FBI.
The FBI has returned the material to the Spanish court investigating the raid and a Spanish judicial source said last week that Spanish authorities had returned the material to Pyongyang's mission.
The anti-Kim group, which also calls itself Free Joseon, said the raid was not an attack. It said had been invited into the embassy.
The incident came at a sensitive time, just days ahead of a second summit between US President Donald Trump and Kim Jong Un at which the US leader failed to make progress in efforts to persuade North Korea to give up a nuclear weapons program.North Korea's foreign ministry denounced the incident as a "grave terrorist attack" and cited rumors that the FBI was partially behind the raid. The US State Department has said Washington had nothing to do with it.