Rhett McLaughlin just got a temporary restraining order against a man whom he claims has threatened seriously violent behavior ... including a terrorist attack on the scale of 9/11.
The comedian/YouTube personality filed the TRO request earlier this month, claiming a man named Josiah Galvin had made repeated threats against him ... with this alleged online correspondence dating back to May 6.
In the docs, obtained by TMZ, Rhett alleges that Galvin threatened to commit a "911 attack" and blow up Rhett's offices -- which he allegedly identified by physical address. Rhett also claims this guy threatened to kill him specifically.
Rhett -- who initially filed the request under seal for fear Galvin might escalate his actions if he learned of the legal action against him -- says he's had to hire extra security for both himself and his company as a result of the threats ... and, he's worried Galvin may attack him or a venue he's performing at during future public appearances.
McLaughlin also filed for and got legal protection for his wife, Jessie, fearing Josiah may try to attack her. The TRO will remain in effect until at least a formal hearing, which is currently scheduled for June 5.
Rhett hit it big on YouTube as part of the internet duo Rhett & Link, created with his childhood friend, Link Neal. The pair founded the production company Mythical Entertainment, which has become one of the largest content creators on YouTube.
They're currently on their "Good Mythical Tour" ... performing at The Wiltern in Los Angeles Tuesday. They're set to perform in Nashville tonight and St. Louis tomorrow.
We've reached out to the Mythical camp for comment ... so far, no word back.