A young US man who admitted decapitating his mother when she asked him to put some boxes away smiled for his mugshot after he was reported to police by his brother.

Christian Jose Gomez, 23, allegedly cut off his mother Maria Suarez-Cassagne's head with an axe at their Florida home on New Year's Eve, local TV station WFTS reports.

Police responded to a call from Gomez's brother Mario and found Ms Cassagne's headless body at the family home.

Police allege Gomez attacked his mother in the garage then placed her head inside a rubbish bin.

He was reportedly unable to stuff the body into the bin so he left it for his older brother to find, who had been in his bedroom during the attack.

Gomez was arrested a few blocks away from the family home where he was riding his bike.

Sheriff Bob Gualtieri said Gomez, who has a history of mental illness, calmly told police he had killed his mother after she told him to move some boxes.

"In a very calm, cool way he explained what he did, why he did it, what happened, and by talking to him you wouldn't know he had any mental illness, he had any trouble at all. And you know that's very scary," Sheriff Gualtieri said.