Fetch your site as Google from GWT and you may see your site could be hacked for showing those content to Google bot.
Hello, There are several possibilities: 1 - Your site is hacked and there are lots of pages which you don't know about with content related to these keywords. Unlikely, but possible. 2 - Someone has created a link network with x-rated anchor keyword, pointing to your website - negative SEO. Solutions: 1 - Check your websites and your scripts. Are there any updates available? If you find any hidden code in your files, consider how it could have gotten there. 2 - Check the links to your website in the Google Search Console (Webmaster Tools). Use the disavow tool to take care of any links you don't like.
It may be in your on page content those keywords are inserted check once your on page content and update it
May be some content containing those keywords are posted in your on page optimization. Once check entire site and content find those keywords. If you don't find those keywords in your website content then give those keywords as negative keywords.