There’s a couple options from before the ps2 standard, but I’d guess it’s a 5-pin DIN connector on an AT keyboard (e.g. IBM model M). You’ll need to know more about the keyboard to make a determination, but you might get lucky with a passive adapter to PS2 and chain to USB. Before the ps2 standard, there was more variety between manufacturers in both signaling and connectors.
There’s a couple options from before the ps2 standard, but I’d guess it’s a 5-pin DIN connector on an AT keyboard (e.g. IBM model M). You’ll need to know more about the keyboard to make a determination, but you might get lucky with a passive adapter to PS2 and chain to USB. Before the ps2 standard, there was more variety between manufacturers in both signaling and connectors.