The mayor is undergoing treatment at a hospital there for cerebral vasculitis or inflammation of blood vessel.
His aide AKM Mizanur Rahman told bdnews24.com on Friday that the prime minister, who went to the UK on her way back home from the US, called and met the members of Annisul's family at Savoy Hotel on Thursday evening.
"They spent a long time together. The prime minister enquired about the mayor's health," he said, referring to phone conversations with Annisul's family.
He said the family told him the mayor's condition was 'improving'.
"He does not need oxygen mask or ventilator anymore for breathing. He is improving. He opens his eyes some times.
"The doctors are giving him medicine, steroids. And those are working. But they said it would take time," Mizanur said.
Annisul was admitted to the hospital on Aug 4. He is kept 'sedated' at the intensive care unit, his family said earlier.