United Liberation Front of Asom military wing leader Ranjan Chowdhury was arrested in Mymensingh district of Bangladesh on Monday.
Chowdhury was arrested from a nursing home in Sherpur where he was undergoing treatment, said a Bangladeshi news agency.
He may be handed over to India, it added.
Chowdhury's wife Sabitri Sangma had confirmed the arrest over telephone Bangladesh's New Age newspaper.
Five ULFA leaders, including its chairman Arabinda Rajkhowa, were arrested and handed over to India earlier this year.
