I frequently hear this.

Problem:
The “at” in this question is unnecessary.

Explanation:
Any time that you see a sentence ending with a preposition, re-word it so that the preposition is not at the end. Trying this with the above question, we get, “At where are you?” With this re-wording, we see that “at” is unnecessary — because “where” implies “at”. Put another way, “where” is conceptually equivalent to “at” plus a location.

Solution:
“Where are you?”