It is indeed Byzantine and that K makes it a half follis. The other side is two seated figures, Justin II and Sofia. The surviving stuff on the reverse is enough to get a full ID:
Justin II & Sophia AE Half Follis. 565-578 AD. Thessalonica mint. D N IVSTINVS P P AVG, Justin on left, Sophia on right, seated facing on double-throne, both nimbate, Justin holding cross on globe, Sophia holding sceptre, sometimes with cross between their heads / large K, ANNO to left, theta-cross-C above, officina letter below, mintmark TES. SB 366 (Type 2 with theta cross C above), MIB 70.
cf. this better example on wildwinds: http://www.wildwinds.com/coins/byz/...66_type2.jpg
Justin II & Sophia AE Half Follis. 565-578 AD. Thessalonica mint. D N IVSTINVS P P AVG, Justin on left, Sophia on right, seated facing on double-throne, both nimbate, Justin holding cross on globe, Sophia holding sceptre, sometimes with cross between their heads / large K, ANNO to left, theta-cross-C above, officina letter below, mintmark TES. SB 366 (Type 2 with theta cross C above), MIB 70.
cf. this better example on wildwinds: http://www.wildwinds.com/coins/byz/...66_type2.jpg





















