If you are a resident of a country and you are not born there, then you can apply for an Iranian Visa. The only extra requisite which will be asked from you is a valid residency permit from the government of the country you are currently residing in.
For example, if you are a citizen of India and are currently living in the USA, then a valid residency permit of the USA (which, in USA�s case is also known as a �Green Card�) is to be submitted along with your application form and other documents.