It depends. If time is linear and only exists in a single reality, sure. But if not, then when someone went back in time they'd have created a parallel reality existing beside the reality we currently experience. For an example, say someone went from the arbitrary year 2100 to 2000.

When he went back to 2000, the timeline would split into two parallel timelines - the history of the first timeline remains unchanged - aka, the time traveler never arrives in his own past. The parallel timeline shares a history with the base timeline right up to the arrival of the time traveler, then it exists separately. This disallows the time traveler from being able to influence his own past since it took place in the base timeline which he is not experiencing.*
The idea isn't that a new reality is created when the time traveler goes back in time, but that there are an infinite number of possible realities, and time travel allows us to travel to different timelines than our own. At least, that's one theory.
I was just pointing out that we're all time travelers in our own timeline, for the lulz.
*This would mean he can't stop himself from making the initial leap through time, but he could possibly stop his alter-self from making a leap through time from the secondary reality to a third reality, or the alter-self could stop his alter-alter-self from leaping from the third reality to a fourth reality, etc.