Nandi Senator Samson Cherargei was on Tuesday arrested on allegation of ethnic contempt and incitement to violence.
The Directorate of Criminal Investigations said the senator will be arraigned over utterances he made in August at Kilibwoni Primary School that bordered on hate speech.
Mr Cherargei was taken to the DCI headquarters on Kiambu Road for questioning.
In August, a video went viral showing Mr Cherargei warning critics Deputy President William Ruto of action.
The senator did not specify what action he would take against the individuals that he did not name.