Ayhan Bilgen, spokesman for the Peoples' Democratic Party, HDP, told The Associated Press that Buldan was taken away for questioning from her home in Istanbul early on Friday.
The state-run Anadolu Agency said she was detained over an on-going investigation into her activities.
Turkey's government accuses the HDP, the nation's third-largest party, of links to the outlawed Kurdish rebels - an accusation the party rejects.
In May, parliament voted to strip lawmakers of their legal immunity, paving the way for the HDP legislators' arrests.
A total of 12 HDP legislators have been jailed on terrorism-related charges since then, including co-leaders Selahattin Demirtas and Figen Yuksekdag.