The son was arrested after the bodies were found soaked in blood. Local media reported that Arshad fed his family laced food and drink before strangling some of them and killing the others with a knife.
His father Badar, who is still on the run, is also suspected to have been involved in the tragedy.
The victims have been named as Alia, nine, Alshia, 19, Aksa, 16, Rahmeen 18, and their mum Asma.
The family had travelled from Agra to Lucknow to celebrate the new year.
In a twisted video circulating social media made after the alleged killings, Arshad claimed he had killed his family to 'protect' them from his family's neighbours, who he claimed were planning on selling his sisters in Hyderabad.