James Howell, 20, was arrested at around dawn in Santa Monica with multiple weapons, ammunition and bomb-making materials in his car, which had Indiana license plates, police said.
The arrest came just hours after 50 people were massacred at a gay nightclub in Florida, prompting fears of a similar attack in Los Angeles.
Santa Monica police chief Jacqueline Seabrooks initially said that Howell told the arresting officers that he wanted “to harm” the annual L.A. Pride parade taking place in Hollywood on Sunday.
However, officials later said that investigators were trying to determine Howell’s intentions and that he had only told police that he planned to attend the parade and made no reference to doing any harm.
“It was a misstatement as chief Seabrooks was given the wrong information,” Santa Monica police lieutenant Saul Rodriguez told AFP.
“(Howell) did not make any additional statements saying he was going to do anything further than attend the parade.”
He said that Howell was being held on $500,000 bail on state charges of possession of firearms and explosives.
Police said in a statement that Howell was arrested after a resident reported a prowler knocking on their door and window at around 5:00 am.
When officers responded, they found Howell sitting in a car with three assault rifles, high-capacity magazines and ammunition, the statement said.
“Additionally, officers discovered a five-gallon bucket with chemicals capable of forming an improvised explosive device,” it added.
Seabrooks said there was no known connection between Howell and the carnage in Orlando, Florida — the worst mass shooting in US history.
Authorities said they had considered calling off the parade but then decided to go forward while beefing up security, including placing undercover police in the crowd.
The march went ahead without incident.
The Los Angeles Times, quoting Indiana court records, said Howell was charged in October 2015 with intimidation and a felony count for pointing a firearm at another person.
Prosecutors dropped the felony charge after he pleaded guilty in April to the lesser misdemeanor charge of intimidation.
As part of his plea deal, he agreed to forfeit all weapons during his term of probation, the Times said.