Very nice, looks authentic. Its from Alexandria and its a bronze tetradrachm of an empress. It appears to read 'VEDINA CEB', indicating this coin to be SEVERINA (The D is actually a Rho (P as it appears int eh greek alphabet, but its an R in the latin) , and the CEB is greek for Augusta). Its got the date on it (the Z being the regnal year) but I couldnt find the corresponding year AD.
The person on the back is Dikaiosyne, the ancient greek equivalent of Justice.
Its a nice coin and Severina isn't a very common person to find on coins either, nice to find lying around.