Generating a Random number in C# with Alpha numeric values

Hi I have write the the method for create random number it's working fine..returning the random number but I have a doubt It may be generate the same number some time.. Please any one give me your suggestion will have chance to generate same number???? if have give me a solution..This is my code set for create the random number

public string GetUniqueKey()
{
        int maxSize = 6;
        char[] chars = new char[62];
        chars = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890".ToCharArray();
        byte[] data = new byte[1];
        using (RNGCryptoServiceProvider crypto = new RNGCryptoServiceProvider())
        {
            crypto.GetNonZeroBytes(data);
            data = new byte[maxSize];
            crypto.GetNonZeroBytes(data);
        }
        StringBuilder result = new StringBuilder(maxSize);
        foreach (byte b in data)
        {
            result.Append(chars[b % (chars.Length)]);
        }
        return result.ToString();
}