Detectives launched a battery probe into the “WAP” star’s actions after she retaliated when a concert-goer chucked a liquid at her.
Footage posted on social media shows the “Money” singer recoiling after someone close to the stage splashed the contents of a cup in her direction.
In the clips, Cardi B can be seen pausing briefly, before flinging the microphone back in the same direction.
However, some videos online appear to show the mic making contact with a different member of the audience.
Las Vegas Metropolitan Police Department said Monday that a woman had contacted them to report a battery, and that they had begun an investigation.
But on Thursday, they confirmed that the probe had been dropped.
“After a thorough review of this case and with the consultation from the Clark County District Attorney’s Office, this case has been closed as having insufficient evidence,” a statement said.
“No charges will be filed in relation to this case.”
Meanwhile, a listing on bidding site eBay for a microphone purported to be at the centre of the drama had reached $99,900 by Thursday afternoon.
TMZ reported the seller, Scott Fisher, works for a company that provides audio kit for Las Vegas clubs.
The entertainment outlet reported Fisher as saying the proceeds from the sale, which ends Tuesday, would be split between two charities — the Wounded Warrior Project and Friendship Circle Las Vegas, which helps teens and young adults with special needs.
The mic-hurl episode was the latest involving performers being the target of objects from the audience.
In June a man threw a phone at Bebe Rexha during a concert in New York, landing the singer in hospital.
The same month an audience member threw a bag purportedly containing the ashes of their mother at the stage while singer Pink was performing in London.
And last year Harry Styles good-naturedly paused a New York concert after someone threw a chicken nugget in his direction.
In December, Guns N’ Roses frontman Axl Rose pledged to stop throwing his microphone into the audience at the end of a show after a fan was reportedly hurt in Australia.