Ahmed was detained from his MLA quarter in Dispur on Saturday and taken to the Panbazar police station for interrogation before being arrested, they said.
He is likely to be produced at the court during the day, a police officer said.
A case under IPC section 124A (sedition) was filed against him, he said.
Several organisations, including the All Assam Students’ Union (AASU) and the BJP’s youth wing BJYM, filed police complaints against the legislator over his remarks.
The state Congress had also issued him a notice for his “communally provocative” statements ahead of the bypolls in the state, and sought a reply within three days.
Ahmed had made the remarks while reacting to assertions by some leaders of the BJP-led ruling alliance that the alleged encroachers in Sipajhar area of Darrang district “had killed” eight people in 1983 during the six-year-long Assam agitation.
Ahmed had allegedly said that the eight people who died in the 1983 agitation were “not martyrs, but killers”, as they were involved in slaughtering people from the minority community of the Sipajhar area where Gorukhuti is located.
He had purportedly said that “the attack” on the eight people was an act of “self defence” by the Muslim population of that area.
In its notice, the Congress said, “As a lawmaker, your communally provocative comments in media, gnawing at old wounds of the past incidents of Assam Agitation when people of Assam across communities had suffered, is totally insensitive and uncalled for.”
The state’s ruling alliance partner, Asom Gana Parishad, born out of the Assam agitation, had organised protests at various places, including Dibrugarh, Barpeta, Mangaldoi, Dhemaji, Tezpur, Biswanath, Nalbari, Bongaigaon, Majuli and Morigaon, and burnt effigies of the Congress MLA.
Two people were killed in police firing during an eviction drive in Darrang last month amid massive protests. Over 20 people were injured in the melee.