The song, Wapo, which has not made it to the radio airwaves yet, emerged last week and was widely shared on social media, especially on Whatsapp.
Part of it asks: "Is there still freedom of expression in the country?”
It makes reference to a doctor who lances boils but cannot tolerate criticism.
President John Magufuli has often spoken of "lancing boils" in reference to his no-nonsense approach to governing.
The police told a local newspaper: "Ney wa Mitego will be questioned for releasing a song with words that malign the government."
The rapper is popular for his scathing lyrics attacking not only the government but even his fellow artists.
On his social media accounts he uses the name Nay true boy (translated from Swahili), saying he always speaks his mind and tells the truth.
His arrest comes just days after President John Magufuli warned media owners to be careful on how they use their press freedom.
-The Star