People you invite to Yelp automatically become your friends. Whenever your friends review a business, their activity appears in a special section of your account. This enables you to quickly comment on your friends' reviews. To prevent from a specific friend from appearing on your account, you need to unfriend him. Deleting friends from your Yelp account takes just a few seconds and the updates stop immediately.
Click your picture after you log in to your Yelp account and choose "Account Settings" from the menu. Click the "Friends" link to view all your Yelp friends. Click the "X" icon at the right of the person you want to remove from your list of friends. Click "Confirm" to confirm and defriend the person.