Mandera Senator Billow Kerrow and three MPs from the region have been arrested.
The four were picked by Flying Squad officers after they landed at Wilson Airport on Thursday morning.
Police sources to the Nation two of the three MPs arrested are Mandera West MP Mohamud Mohammed and his Mandera East counterpart Abdiaziz Ali Farah.
The lawmakers were taken to the Directorate of Criminal Investigations (DCI) headquarters where they are being grilled by the Head of Investigations Mr John Kariuki
Sources say they are being investigated for incitement to violence and giving false information.
The leaders were arrested a day after they apologised for claiming that mass graves have been discovered in Mandera.
Mr Kerrow said only one body was found at the site of the alleged mass grave and regretted the anxiety and panic caused by the remarks.