MNS spokesperson Sandip Deshpande and some others were picked up from Dadar and later whisked off to the nearby Shivaji Park Police Station.
Strongly protesting his detention, Deshpande termed it as "high-handed action" by the police.
The MNS activists were already served notices warning them against creating any law and order issues before Thackeray's appearance in the Enforcement Directorate office in South Mumbai.
Thackeray has issued at least two direct appeals to all his followers to remain calm despite any provocation, keep away from the ED office, and desist from any form of agitation or violence.
Thackeray is expected to reach the ED office around 11 a.m. to respond to the summons served on August 18.
His former business partners Unmesh Joshi son of former Lok Sabha Speaker Manohar Joshi and Rajan Shirodkar, have already been grilled by the ED in a case pertaining to the IL&FS imbroglio.
Not taking any chances, the Mumbai Police have implemented tight security measures in the vicinity of the ED Offices in South Mumbai, with a huge force deployed, roadblocks, barricades, restricted entry of people, etc.
On Wednesday, agitated by the Enforcement Directorate (ED) summons to the MNS chief, a young party activist committed suicide by setting himself on fire.
( With inputs from IANS )