To block someone's posts from your dashboard on Tumblr, you have to add the account to your block list. However, blocking an account also forces you to unfollow it. Although Tumblr doesn't give you the option to block someone's posts and keep following him, you can use a Web browser extension to get the job done. The extension is free and hides posts from specific people based on custom keywords. Tumblr still displays the posts, but the extension hides them at the Web browser level.
Hiding Tumblr Posts
On Tumblr, you can't block a member's posts without unfollowing him. To work around this issue, install the Tumblr Savior extension (see links in Resources) in Google Chrome, Mozilla Firefox, Safari or Opera. Click the Tumblr Savior button that was added to your Web browser to display the settings window. Find a unique word that appears in all the posts you want to block and type it into one of the fields in the Black List section. Often, the keyword you're looking for is the Tumblr name of the person you wish to block. Click the "Save" button to filter the posts and then close the settings window. You can display any of the posts by clicking the "Click to show" link.