That appears to be from Pergamon in Mysia, struck under the magistrate Diodoros. It's quite an attractive coin, I don't consider most Pergamon bronzes to be particularly appealing but yours is nice. I don't think it's rare but it's definitely a better example of the type.
I have to disagree with my friend @Plumbata. I find many coins from Pergamon attractive such as your example and this one PERGAMON MYSIA AE15 OBVERSE: Helmeted head of Athena right REVERSE: Head and neck of a bull right "A" above Struck at Mysia, Pergamon 310-283 BC 3.09g, 15mm SNG France 1571. Ex Malloy Auction LXVII,93 Ex Aegean Numismatics and this one: PERGAMON MYSIA AE15 OBVERSE: Helmeted head of Athena right REVERSE: Head and neck of a bull right "A" above Struck at Mysia, Pergamon 310-283 BC 3.09g, 15mm SNG France 1571. Ex Malloy Auction LXVII,93 Ex Aegean Numismatics
