In February last year, a car laden with explosives was found near the Ambani home. The purported owner of the vehicle was later found dead, with police treating his death as suspicious.
Reliance said a call centre run by a company foundation's hospital received two phone calls on Wednesday threatening to blow up the hospital and kill Ambani, his wife Nita and sons Akash and Anant. The caller also threatened to blow up the Ambanis' high-rise family residence Antilia in Mumbai.
"Acting swiftly in the incident of threat calls to Ambani family, a team of Mumbai Police has detained a person from a block in Darbhanga, Bihar at midnight with help of Bihar Police," Mumbai police said in a statement.
"Further investigation is being done in this matter."
Ambani, with a net worth of $87 billion according to Forbes, is India's second-richest person, having been recently dislodged from the top by Gautam Adani.
The Reliance group is involved with telecoms, retail, renewable energy and petroleum products.
(Reporting by Rajendra Jadhav and Shivam Patel in New Delhi; Editing by Peter Graff and Nick Macfie)
