If the adverts Google AdSense is putting on your site aren’t relevant to you site content then possibly Google hasn’t crawled and indexed your site yet. Google can take a while to crawl your site and “register” what your content is about.
Adsense Ads should become more relevant as time passes and as Google works out what your site is about.
Google has some useful information in their Adsense Help Centre. Check out the section “Why Aren’t My Ads Relevant”
Adsense can place adverts based on the following:
- Your on-page content (meta tags, h1, bold words, etc.)
- What the user has visited and clicked on in the past. In this case the adverts are likely to be completely irrelevant to your site. E.g. if you visit Dell to look a PC, then for a while afterwards Google Adsense will display Dell adverts to you, regardless of which site you are currently on. i.e. completely irrelevant adverts for the site you are on