Hello,

Yes you can sit for the JEE Main exam which is conducted for admission to IITs even if your have a Nepal board certificate as long as you have taken at least 5 subjects in your 12th standard examination. These 5 subjects should include Mathematics, Physics, Language and either Chemistry, Biology or a technical vocational subject along with one other exam of any subject. 

For more details on the eligibility criteria for JEE Main, visit: 

https://engineering.careers360.com/articles/jee-main-eligibility-criteria