Efforts to reach Mr. Olsen’s family on Tuesday evening were unsuccessful.
The F.B.I. did not immediately respond to requests for comment Tuesday evening.
The agency said in the court filing that in March, agents in Alaska found that the online account associated with Mr. Olsen “showed a large increase in subscribers” from the previous month. He had 4,400 followers on iFunny, a website and mobile application where users can share photos, videos and messages, according to the filing.
A message posted by the account in August suggested that people should not comply with gun laws, according to the court filing. “Stock up on stuff they could ban,” the post reads. “In fact, go out of your way to break these laws.”
“Even the Oklahoma City bombing shows that armed resistance is a viable method of political change,” Mr. Olsen posted online, according to the affidavit, apparently referencing the 1995 bombing that killed 168 people. “There is no legal solution.”
Mr. Olsen was living with his father in Boardman at the time of his arrest, according to the affidavit. On Aug. 7, the authorities arrested Mr. Olsen as he was leaving the home.
That same day, federal investigators searched the home. In one bedroom, they found 10,000 rounds of ammunition, camouflage clothing and backpacks, according to the court filing. In the trunk of Justin Olsen’s car, investigators found a machete.
In Mr. Olsen’s father’s bedroom, investigators found AR-15-style rifles and shotguns.
The authorities seized 15 rifles, several shotguns, 10 semiautomatic pistols and 10,000 rounds of ammunition from the home, according to the affidavit.
The next hearing in Mr. Olsen’s case is scheduled for Aug. 16.
Sheelagh McNeill contributed research.