The following countries do not need a visa.
Armenia, Azerbaijan, Cuba, Ecuador, Georgia, Israel, Kazakhstan, Korea (Democratic People's Republic), Kyrgyzstan, Moldova, Mongolia, Qatar, Russia, Serbia, Tajikistan, Turkey, Ukraine, United Arab Emirates, Uzbekistan and Venezuela.
Everyone else has to get a visa in advance and you probably need an invitation/tourist voucher. You can get a visa on arrival at Minsk airport if you have an invitation that you have organised in advance.
A transit visa may be easier to obtain but it may be more expensive depending on your passport.
Full story on Visa requirements