The pair will meet at the Veltins Arena on February 26 before the second leg takes place at the Santiago Bernabeu on March 18.
Keller believes the draw is a positive for Schalke and expects his charges to relish pitting their wits against the nine-time European champions.
"It's a great draw for us and our fans," he said.
"It's a fantastic challenge for our players to play against the most famous club in the world with players such as Cristiano Ronaldo, Iker Casillas and Gareth Bale. We are really looking forward to it."
Captain Benedikt Howedes believes the Gelsenkirchen club can cause an upset, despite Madrid's tag as heavy favourites going into the match-up.
"I am pleased with the draw of Real Madrid, it is too bad that Sami Khedira can not be there due to his injury," he said. "To play at the Bernabeu is something completely new for me.
"Even if Real are the absolute favourites, I see an outside chance for us."
Schalke attacker Julian Draxler has been linked with a host of clubs in recent months, including the Blancos, and he believes that playing against Carlo Ancelotti's men in Madrid will be a dream fulfilled.
"This pairing is a real Champions League highlight," the 20-year-old said. "It has always been my dream to play once against Real Madrid at the Bernabeu.
"It could not have been much more difficult a draw but we will face the task at hand. I look forward to the two games."