Hacked into my e-mails?

I went on my Yahoo e-mail account and was trying to clear up my folders and I noticed in SENT folder there was some e-mails that had been sent to a couple addresses. The e-mails were not junk e-mails. I could still log in so my password was not changed.
So my question is, if your e-mail account is hacked into from another computer would the e-mails show up in the SENT folder?
Or is someone hacking my account from MY COMPUTER???

The emails are stored on their server, not your computer. If there is sent mail you didn't write, real easy to fix the situation. Change your password.

thank you so much . . . already have!!!

It could also be a virus that is multiplying itself by using your e mail to sends itself to other e mail clients.