The reverse matched AMNG 630 however that one has a diademed bust obverse while mine is a helmeted bust. No perfect matches there. But since the reverse fits the description of 630, it would probably be from the same time period; so Gordian III 238-244 AD. Correct me if I'm wrong.
KOINON MAKEΔONΩN B NEΩKO Athena seated left, holding helmet in outstretched right hand, resting left arm on shield behind.