Sources said Mehbooba was arrested on the orders of the Executive Magistrate in Srinagar and shifted to Hari Niwas guest house.
In his order, the First Class Executive Magistrate cited apprehensions of law and order situation and breach of peace and tranquillity in Kashmir.
"Your (Mufti) activities are likely to cause breach of peace keeping into consideration your recent activities that may likely lead to serious law and order situatuion and breach of peace and tranquillity in Kashmir," the order said.
It said Mehbooba and her party activists were about to proceed in a procession in public which could threaten law and order. "Keeping into consideration the present situation in Kashmir...I do hereby immediately order your detention," said the Executive Magistrate.
Earlier in the day, Mufti described scrapping of Article 370 of the Constitution which gave special status to the state as the "blackest day in Indian democracy". The government earlier in the day revoked the state's special status, provided under Article 370, via a Presidential order.
Hitting out at the government, Mufti in an audio message on Twitter said Parliament which gave a lot to Jammu and Kashmir "has snatched everything from it like thieves". "Today is the blackest day in Indian democracy. The Indian Parliament just like thieves today snatched everything it has given," she said.
The former Chief Minister had been under house arrest since Sunday evening. She said the security forces were increased in Jammu and Kashmir in recent days on the pretext of security threats to the Amarnath Yatra and tourists from Pakistan. "Such a big country got frightened ... and made Kashmir an open jail so that no one can raise voice against the illegal proposal," she said.
The PDP leader said that "we had good relations which the government" but said this had changed just like Israeli government changed it to illegal occupancy.
"Today people of Jammu and Kashmir are forced to think that the decision of our leaders to reject Pakistan and join India was not right. The conditions with which we joined them have been broken by India. For the respect and dignity of Kashmir, we have no other way," she added.
The PDP leader also said that the decision to revoke Article 370 will have "catastrophic consequences".
"The decision of the J&K leadership to reject the two-nation theory in 1947 and align with India has backfired. Unilateral decision of GOI to scrap Article 370 is illegal and unconstitutional which will make India an occupational force in J&K," she tweeted.
"It will have catastrophic consequences for the subcontinent. GOI's intentions are clear. They want the territory of J&K by terrorising its people. India has failed Kashmir in keeping its promises," she said.
( With inputs from IANS )