Yes – if you do it within a short period of time.

When you delete a contact in Yahoo! Mail, it goes the Trash folder in your Yahoo! Address Book (http://address.yahoo.com). Trash is on the left side of the page. See it?

Click Trash to open it, and when you find the contact you didn’t mean to delete, click it once. Then click Restore to put it back in your Contacts folder.

Remember that contacts in Trash can be deleted at any time, without warning. So if something accidentally ends up there, go get it quick! Once trash is emptied, anything in it is permanently deleted from the Yahoo! Address Book server and cannot be recovered.