Narayan Pandey, a follower of the self-styled godman, was arrested by the Sadar Bazar police of Shahjahanpur in connection with the murder of Kripal Singh, police said.
Pandey, who admitted to his role in Singh's murder, was produced in the court and sent to jail, they said.
Singh was on July 10 shot by motorcycle-borne assailants in Cant police station area. He had been Asaram's disciple in his Jodhpur ashram and was called in Shahjahanpur with the help of Jodhpur Police.
It came to light during interrogation that Singh was shot by professional shooters while Pandey and three others had hatched the conspiracy.
They had earlier tried to buy over Singh by offering Rs 10 to 20 lakhs but he did not relent and as the last resort he was eliminated, police said.
Singh was a key witness and his statement in the case against Asaram had been recorded some three months ago.
Asaram has been in a jail in Jodhpur since September 2013.
Two months later, he, along with his son Narayan Sai, was booked for the alleged rape of two sisters at their ashram in Gujarat's Surat.
In the last attack against Asaram's witness, his cook was shot dead in Muzaffarnagar in Uttar Pradesh in January.
Nine witnesses have been attacked so far and two have died.
Rape victim's father gives audio clip against Asaram to police
Witness in Asaram case dies, hunt on for assailants
CBI should probe murder of witness in Asaram case: UP govt
SHOCKER! UP Journalist's mother 'set ablaze' by 2 cops
Witness in Asaram molestation case shot at