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 and highly-rated winger Julian Draxler are also eager to face Real, who finished Group B unbeaten.
Howedes told Schalke's official website: "I am pleased with the draw of Real Madrid, (it is) too bad that Sami Khedira can not be there due to his injury. To play at the Bernabeu is something completely new for me.
"Even if Real is absolute top favorite, I see an outside chance for us."
Twenty-year-old Draxler, who has been linked with a host of clubs in recent months, including Real, added: "This pairing is a real Champions League highlight.
"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 face the task. I look forward to the two games."
