The 98th Academy Awards are scheduled to take place on Sunday at the Dolby Theatre, Hollywood, with O'Brien, 62, hosting the ceremony attended by leading nominees including Jessie Buckley and Timothée Chalamet.
Variety recently reported security is on a heightened alert after the FBI warned California law enforcement about the possibility of a retaliatory drone attack by Iran targeting the West Coast.
A private security contractor who works with several A-list celebrities expected to attend the ceremony has now told RadarOnline.com anxiety is spreading among those preparing to walk the red carpet.
The source told the outlet: "There is genuine unease behind the scenes because everyone understands the Oscars is one of the most visible events in the world. If someone wanted attention, that stage would deliver it.
"Clients are now asking detailed questions about evacuation routes, airspace monitoring and how quickly the venue could be locked down if something appeared in the sky.
"No one is saying the threat is certain, but the fact federal agencies issued the alert has made people jittery."
Radar also reported law enforcement agencies across California have moved to reinforce security around other major gatherings as tensions rise following the escalating conflict between Iran, the United States, and Israel.
It added officials say surveillance, intelligence sharing, and protective measures have been expanded around the Oscars venue.
They are said to include increased patrols, controlled perimeters, and specialist response units.
The outlet said: "Authorities emphasise there is no confirmed plot targeting the ceremony itself, but they say the alert has prompted heightened vigilance as Hollywood prepares for one of its most globally watched nights in showbiz."
