The 26-year-old made the move from Scottish side Motherwell last summer and has impressed during his first season at the Kassam Stadium, scoring nine times and racking up 13 assists.
Johnson's good performance in League One have reportedly caught the eye of West Brom and Midlands rivals Aston Villa and Birmingham City.
Albion are thought to have sent scouts to watch the winger in action but Johnson says he knows nothing of the reported interest in him, claiming he is just focusing on his performances for Oxford.
"For people to be talking about you then you must be doing something right," he told the Oxford Mail. "It’s just rumours and you have to get on with your football.
"You just have to keep your head down and keep doing what you’re doing. The more you see it, the more it should push you on."