The former couple was staying away from each other when they unintentionally showed up at the same party hosted by Bootsy Bellows-owner Markus Molinari, reported Ace Showbiz.
According to a partygoer, Schwarzenegger and Cyrus, 22, were seen avoiding each other during the birthday party taking place at Blind Dragon in West Hollywood on May 29.
"Patrick and Miley didn't interact. He didn't say a word to her," the source said.
The "Wrecking Ball" hitmaker and Schwarzenegger called their relationship quits in April after five months of dating. The pair were hit with various rumours including fighting and cheating.