Social activist Medha Patkar was on Wednesday arrested on her way to Singur, the site for the Tata Motors small car project in Hooghly district, police said.
Patkar was arrested along with five other leaders of the National Alliance of People's Movement, an NGO, near Metropolitan township on E M By-pass.
They were later taken to an office of the youth affairs department in Salt Lake, they said.
The police, however, sighted no reason for their arrest.
The arrest was made as soon as Patkar along with other NAPM leaders left for Singur to meet the farmers there.
Earlier, Patkar demanded scrapping of the Special Economic Zone Act and the Land Aquisition Act in the interest of farmers, while calling for meaninful utilisation of vacant land for industry and setting up of agro-industries in the country.