did you check like site:
www.yourdomain.com or link:
www.yourdomain.com in yahoo? If it's true, then there is some problem with your pages. If you search any other keywords in yahoo, then that's normal. Based on the keyword you're searching, yahoo will pick some other texts from your page to show as title and description.
BTW, yahoo and MSN place less importance on meta description and keyword tag than google.