Comment on Google AdSense Ad Channels by SEO Dave.
That doesn’t mean you’ll agree all the ads are related to the content, but Google AdSense isn’t randomly showing ads.
Exception to this is on a site that’s just had AdSense ads added to and where you are seeing Public Service ads (charity ads). Give it time and it normally gets better.
You can add code to your site to suggest to Goggle AdSense which content of your page to use as the basis for ads: see Targeting AdSense Ads to Make More Money. Note to my theme users, this code is built into the themes.
You can also write your content to target keywords you’d like ads for. If you want ads related to finance for example and never mention money, finance and similar keywords on the page don’t expect AdSense ads related to finance.