The 59-year-old Beal was handcuffed and only spoke to answer questions from the judge. Another hearing was scheduled for Monday, when attorneys will discuss bail and scheduling.
Orange County sheriff's officials said late Tuesday night that they had not found a specific explosive device and were continuing to sift through the debris left from the explosion.
Barnes said an explosive device went off inside the day spa shortly after 1 p.m. Tuesday.
Their description was included in documents released by federal prosecutors on Thursday.
The cause of the blast remained a mystery for much of the day, with officials initially believing a vehicle had smashed into the building.
Police on Wednesday searched Beal's home on warrants involved in Ildiko Krajnyak's death.
Beal is awaiting a court appearance after being charged with possessing a destructive device.
The former boyfriend of a woman killed in an explosion in Aliso Viejo has been arrested.
The officials said the explosion did not appear to be part of a broader plot and there was no immediate connection to any extremist groups.
Authorities have declined to say if they believe the victim was the target.
They remained business partners, with Beal serving as spa manager, and the two operated a separate cosmetics firm.
A phone message seeking comment from Beal's public defender was not immediately returned.
Photos on his Facebook page showed them living it up in far-flung places: a beach in Cuba, restaurants in Portugal, and riding jet skis in Mexico. Beal seemed happier after meeting Krajnyak and spoke of her frequently. Don Westerhoff said Beal told neighbors that the pair had been moving a heavy cabinet downstairs, when Beal lost his grip on the furniture and it slid down the stairs, slamming into his wife.
Beal's son, Nathan, says his father and Krajnyak had recently broken up.
The Latest: California office blast victim ran day spa
The Orange County Sheriff's Office said Tuesday night it had "not determined conclusively whether the explosion was accidental or intentional".
A woman who was on her way to an appointment in the area told CBS2 she arrived just after the blast occurred, and she saw fire on the roof of the building.
Krajnyak, 48, owned a day spa in the building, which is located roughly 50 miles south of Los Angeles.
Almost choking up at times, he said he had visited his sister for two weeks last month in order to help her with her business. Last month, he had come to the U.S.to help with her business that offered services such as facials, waxing and wrinkle treatments.
Krajnyak was killed and two other women, who were customers at the spa, were seriously injured.
Beal, a model rocket hobbyist, told investigators he had not made any bombs and did not have material for an explosion as powerful as the one he saw in news coverage.
"Anytime you see an explosion of this magnitude, it would definitely be suspicious to us", Sawyer said.
Children at a day care facility across the street from the building were evacuated. The son told Davis that they built movie props, he said.
Paul Delacourt, assistant director in charge of the FBI's Los Angeles field office, said the "working theory is this explosion was caused by a device", and he reiterated that investigators "do not believe this was an accident".
Eimiller stressed that Beal was not being held in connection with Tuesday's explosion.
Eimiller says no additional details will be provided until a federal criminal complaint is released.
According to the Federal Bureau of Investigation affidavit, one of the injured women told investigators that while she was at the spa, she noticed "lots of mail piled up along with three to four brown cardboard boxes on the floor next to the counter".
Officials haven't formally identified the body but said Wednesday they believe it is that of Ildiko Krajnyak (IL-di-koh KRY-nyak), a licensed cosmetologist.
The Tuesday blast sent plumes of white smoke into the air and debris flying into the parking lot.