Yes, you need visa and can obtain on arrival at Kathmandu airport and other boarder entry points (need a pair of passport size photo with clear background) or Nepalese embassies and consulate offices abroad. You can also apply on line: http://www.nepalimmigration.gov.np
Visa Fee: For 15 days (US$ 25), 30 days (US$ 40) and 90 days (US$ 100) payable in cash.
For multiple entry; US$ 20.
Now, Nepal Immigration Mobile App can be downloaded from Google Play Store.