The TV and radio presenter's lawyers obtained the stay-away order hours after they say Chidi Benjamin Uzomah Jr. was detained at the E! Entertainment Television headquarters in Los Angeles.
The filing claims Uzomah was carrying a knife and was trying to see the popular television and radio host.
Uzomah, 25, is on probation for another incident involving Ryan. Court records show he pleaded guilty last month to three misdemeanours carrying a switchblade knife, assault and battery. Uzomah was charged after he attacked one of Ryan's bodyguards outside an event.
"His aggressive and violent efforts to come into physical contact with me are extremely frightening to me," Seacrest wrote in a declaration filed last week. "They have jeopardised not only my personal safety, but also the safety and well-being of those around me."
Police said Ozomah was arrested and booked on suspicion of stalking.
The filing states Uzomah tried to meet Ryan at radio station KIIS-FM earlier this month, but Ryan records his show at the E! Entertainment Television headquarters. Besides working as the host of American Idol, Ryan has numerous other gigs, including producing E! series such as Keeping Up With the Kardashians.
A court hearing on whether to grant a three-year stay-away order against Uzomah will be held on November 17.