Gyani Keta,

Toursist visas for the US issued from Nepal are usually for 5 years, although in very few cases people are issued Tourist visas for less period of time. Check the validity of your Visa. If your visa is valid, you do not need to go anywhere and can easily travel to the US; if you Visa has expired, you will need to go to the Embassy and get another one.

There should be something like "Valid Until" or "Valid For" or some thing like this on this, which will determine if your Visa is still valid. Good Luck!