Law enforcement sources tell us Keya Morgan was taken into custody Saturday morning in Scottsdale, AZ -- this after a warrant was issued for his arrest last week. The circumstances surrounding his arrest remain unclear for now.

As we reported ... a judge issued the warrant after Morgan was charged with 5 separate counts of elder abuse out of LA County. The docs stated that the alleged misconduct took place in June 2018, but Stan himself wasn't named as an alleged victim.

It ain't hard to connect the dots here though -- Stan's team filed a restraining order against Morgan a month later, July 2018, claiming the guy had mishandled more than $5 million of the Marvel legend's money ... and that Stan had suffered physical and emotional injuries at the hands of Morgan, who was looking over him around that time.

Keya issued a statement to us last year, completely denying the allegations against him and vowing to clear his name. He said, "This is a witchhunt by his daughter and her lawyer against me because she cannot stand the fact Stan likes me so much. I will 100% prove beyond a shadow of a doubt that the allegations against me are false. The truth will come out."