The 22-year-old has been a mainstay of the United team as they have made it to the last 16 of the Champions League, the last eight of the FA Cup and opened up a 12-point gap at the top of the Premier League.
The Brazilian international is pleased with his form but insists that he still wants to improve.
When asked if this is his best season, Rafael told MUTV: "I think so.
"I have played many games very consistently so it is probably my best season here.
"Of course, I think there are some games where I feel I could have done more, I should have done this or should have done that better. I definitely still want to improve."
Rafael is currently part of the Manchester United side who are facing Queens Park Rangers this afternoon.