Afzal Usmani, allegedly a member of a home-grown Islamist group known as the Indian Mujahideen, was appearing in court to hear prosecution charges against him, according to local media reports.
"He has escaped. The police, everybody is looking for him," Mumbai's anti-terror squad chief Rakesh Maria told AFP.
Usmani was arrested in 2008 for his alleged involvement earlier that year in serial blasts in western Gujarat state which killed 56 people.
He is accused of being part of another attempted bombing in the same state, reports said. It was not immediately clear how Usmani had escaped amid heavy police security at the court.
