Absolutely. You can prepare for the toughest exam in the country - IAS exam without enrolling in a physical classroom. In fact, there are ample online coaching institutes that provide IAS exam online coaching. These classes are available at a price and some even provide classes for free. You can also check out YouTube videos where you will find topic-specific explanations. There is free material available all over the internet also. In fact, many successful candidates have prepared through the help of online coaching.