Sky Sports says Mourinho has accepted a two-year contract offer from Benfica and an announcement is due imminently.
After the dismissal of former coach Bruno Lage, Benfica president Rui Costa declared his replacement would be appointed by the weekend.
Mourinho began his senior coaching career with Benfica before moving onto Porto and then to Chelsea. He touched down in Portugal on Wednesday.
Speaking to the media as he arrived on Wednesday evening with a Benfica scarf draped over him by fans, former Real Madrid and Manchester United manager Mourinho said: "I have nothing to tell you.
"Before I got on the plane, they asked me if I might be interested. I said yes, I might be interested.
"Benfica officially asked me if I would be interested and said that when I returned to Portugal, I would be happy to speak with people. If I return to Benfica, it won't be a career celebration, nor 25 years later, nor a return home.
"I left my previous club four weeks ago. If you ask me if I expected to stay until the end of the season without coaching, that's not in my nature. I wanted to join. I didn't want to say yes to a club that wasn't the right one, just because I'm a workaholic.
"When I was faced with the possibility of coaching Benfica, I didn't think twice about it, saying, 'I'm interested, I'd like it'."
Meanwhile, on Thursday morning, Benfica announced negotiations with Mourinho were underway.
A short statement read: "Sport Lisboa e Benfica – Futebol, SAD informs that negotiations are taking place for the hiring of coach José Mário dos Santos Mourinho Félix, which are expected to be completed soon."