R.K. Mishra, a 1986 batch Indian Police Service (IPS) officer, was served the notice for his speech at a function in Darbhanga district in November held to mark the death anniversary of noted Mithila poet Vidyapati.
He reportedly cited the example of Modi's address in Maithili language at a rally in Patna Oct 27 last year, to exhort the masses to champion the cause of the language.
Mishra could not be contacted despite repeated attempts.
Mishra joined Central Reserve Police Force (CRPF) as inspector general
According to police officials, Mishra replied to the show cause notice on Monday before leaving for Delhi to join the Central Reserve Police Force (CRPF) as inspector general.
He was served the notice a week ago when he was additional director general (modernisation), after the state government received a home ministry letter Dec 27 asking for relieving him. The state government relieved him Jan 13.
"Mishra was served a show cause notice for addressing a public meeting," home secretary Amir Subhani said on Wednesday.