Ya. It's kinda special because in some conjugations the vowel changes (in a regular way) in negative grade, so in a way nothing of the original stem is left:
Anha (vos) ok
Yer (vos) eo
Me (vos) eo
Kisha (vos) oki
Yeri (vos) eo
Mori (vos) eo
The past negative singular is just o, eg. Me vos o. - She didn't go.
We have even nice example from the show's dialogue:
Drogo: Ohos! Os! - Be Still. Don't move.
The words are in infinite oholat - to be still (conjugated to positive grade imperative (though the word is itself probably a semantic extension from negative comparison declension of holat)) and elat (conjugated to negative grade imperative and dropping the vos because it's kinda sorta superfluous).
To contrast the amazingly, deceptively regular elat, Dothraki's other super short word, tat, actually has slightly irregular conjugation, but as usual, this only affects the past singular.