RC4 is one of the most widely used cryptosystem by many applications. It is used for secure communications; file encryption, Secure Sockets Layer, Wired Equivalent Protocol, potentially useful in many popular systems, it is a random bit generator. In this paper, we analyze the linear relationship in the output of RC4 over a large number of keys. In our method we test linear functions of the keystream. For each such linear function, we run the RC4 algorithm on a large randomly chosen set of keys and evaluate the corresponding output. Using statistical test we find that on some output of the RC4, the combination of output bits is not truly random.