Membership in Mensa is open to persons who have attained a score within the upper two percent of the general population on an approved intelligence test that has been properly administered and supervised. There is no other qualification or disqualification for initial membership eligibility.
The term "IQ score" is widely used but poorly defined. There are a large number of tests with different scales. The result on one test of 132 can be the same as a score 148 on another test. Some intelligence tests don't use IQ scores at all. Mensa has set a percentile as cutoff to avoid this confusion. Candidates for membership of Mensa must achieve a score at or above the 98th percentile on a standard test of intelligence (a score that is greater than that achieved by 98 percent of the general population taking the test).
Generally, there are two ways to prove that you qualify for Mensa: either take the Mensa test, or submit a qualifying test score from another test. There are a large number of intelligence tests that are "approved". More information on whether a test you have taken is approved, as well as information on the procedure for taking the Mensa test, can be obtained from the nearest Mensa office. There are no on-line tests that can be used for admission to Mensa. Feel free to contact Mensa for specific details about eligibility.