Villa have won nine of their last 12 games - including the last three on the spin - to climb to fourth in the Championship table.
“Friday is a massive game," Johnstone said.
“Coming off the back of three straight wins, hopefully they are more scared of us. It's all about confidence.
“If you are full of confidence it is a different game. We will be up for it, hopefully we can get three points."
Villa's excellent run has seen them already reach the same number of away wins they managed last term - four - while Villa Park is starting to become a fortress again.
“It's just football," Johnstone, on-loan from Manchester United, said. “It was difficult at the start of the season but we put a few results together and it does give you confidence going into each game.
“Three points are all that matters. I'm glad we are winning both home and away."