Mr Paddock was detained on Wednesday morning on suspicion of crimes related to child pornography.
A source who requested anonymity said Mr Paddock was taken into custody on Wednesday morning.
The Los Angeles Police Department (LAPD) said a man was detained in the 5300 block of Laurel Canyon Boulevard on suspicion of crimes related to child pornography, although the force would not reveal the name of the man.
News of Mr Paddock’s arrest was first reported by TMZ, who said he was taken into custody at an assisted living facility in North Hollywood, Los Angeles.
It said that police obtained a warrant after allegedly being told that material relating to child sex abuse existed on his computer.
Another of Las Vegas killer’s brothers, Eric, spoke to media after it emerged that Stephen was the man behind the deadliest mass shooting in US history.
Mr Paddock killed 59 people and injured more than 500 other when he opened fire on a music concert in Las Vegas from his 32nd-floor hotel room.
He later turned the gun on himself.
In the days that followed, dozens of firearms were discovered in Mr Paddock’s home and vehicles, along with more than 20 in his Mandalay Bay hotel room.