An email seeking comment from his public defender Matthew Terry was not immediately returned.
Alexander was Spears' first husband. The two were married for less than three days in 2004 before an annulment.
Spears, 40, and Asghari, 28, were married Thursday at her home in Thousand Oaks, California, in front of several dozen guests including Selena Gomez, Drew Barrymore, Paris Hilton and Madonna.
Alexander, who was a childhood friend of Spears, was streaming live on Instagram when he approached house. He appeared in a mostly empty but decorated room, telling security Spears had invited him.
Deputies responding to a trespassing call detained him, and he was arrested when they learned he had a warrant for his arrest in another county, the Ventura County Sheriff's Office said.
Spears was previously married from 2004 to 2007 to Kevin Federline, with whom she shares two sons, ages 14 and 15.
She met Asghari in 2016 on the set of the video for her song “Slumber Party.”
Their wedding came nine months after Spears and Asghari were engaged, and nearly seven months after Spears won her freedom from a court conservatorship that controlled her life and affairs for more than 12 years.
Spears posted about the nuptials on her Instagram and Twitter accounts the following day.
"Wow !!! Holy holy crap !!! WE DID IT !!! WE GOT MARRIED !!! Gggggeeeeezzzzz !!! It was the most spectacular day !!!" Spears said in the posts along with a picture of her and Asghari from the wedding. "The ceremony was a dream and the party was even better !!!"
Dalton reported from Santa Monica, California.
Follow AP Entertainment Writer Andrew Dalton on Twitter: https://twitter.com/andyjamesdalton