Mitra/Mittra/Mitter is a common Hindu (religion) surname found in Eastern India (West Bengal) and also in Bangladesh. They mostly belong to the caste Kayastha.
http://en.wikipedia.org/wiki/Mitra_(surname)_
According to legend, five Kayasthas migrated to Bengal around 1050 AD 1. Purushottama Datta (Dutta) 2. Makaranda Ghosh 3. Dasartha Basu(Bose) 4. Kali Dasa Mitra 5. Virata (Dasaratha) Guha
The Mitras claim that they all descended from Kalidasa Mitra and within the Kayastha community they belong to the highest kulin sub class along with Ghosh, Guha and Bose.