If you’d like to prevent Google from combining this potentially sensitive data with the information it has collected from your YouTube, Google+, and other Google accounts, you can remove your Web History and stop it from being recorded moving forward.
After signing into your Google account, type https://www.google.com/history into your browser. (Alternatively, you can choose Account Settings from the pull-down menu in the upper-right corner of a Google product such as Gmail, Google+, or Google.com. From the Account Settings page, scroll down to the Services header and click on the “Go to web history” link.) If your Web History is enabled, you’ll see a list of recent searches and sites visited. Click the gray Remove all Web History button at the top of the page and a subsequent OK button to clear your Web History.
This action also pauses the Web History feature so that it will no longer track your Web searches and whereabouts. If you’d like to fire it back up, simply click the blue Resume button.
(Source: Electronic Frontier Foundation)