I did a deep dive analysis of this organic traffic from irrelevant keywords again and came to a conclusion that it is coming from a particular Internet Service Provider(ISP) and that too from a particular location only. In-order to explore more in detail, i monitor real time data in Google Analytics for organic traffic in that particular location and i found the same (screenshot attached). As a preventive measure, i have implemented a filter in the GA profile by excluding searches from that Internet Service Provider in GA reports. But this does not seems to be a permanent solution to this issue.
Can anyone suggest a solution to fix this issue permanently?