Because it was cold, the servants and officers were standing around a charcoal fire they had made to keep warm. And Peter was also standing with them, warming himself.
KJV
And the servants and officers stood there, who had made a fire of coals; for it was cold: and they warmed themselves: and Peter stood with them, and warmed himself.
ASV
Now the servants and the officers were standing there, having made a fire of coals; for it was cold; and they were warming themselves: and Peter also was with them, standing and warming himself.