The 2018 FIFA World Cup is the 21st FIFA World Cup, a quadrennial international football tournament contested by the men's national teams of the member associations of FIFA, is currently ongoing in Russia starting from 14 June and will end with the final match on 15 July 2018.
This is the first World Cup to be held in Eastern Europe, and the eleventh time that it has been held in Europe. For the first time the tournament takes place on two continents – Europe and Asia. All of the stadium venues are in or just outside European Russia to keep travel time manageable. At an estimated cost of over $14.2 billion, it is the most expensive World Cup in history.
(Only) five Asia Pacific countries are competing in this so-called "world's largest single event", they are Japan, South Korea, Iran, Australia and Saudi Arabia. Football is the most popular sport in nearly every Asian country, and 12 members of the Asian Football Confederation (AFC) have competed at the World Cup since it was first held in 1930 in Uruguay.

1938: The first Asian nation at the World Cup
The Indonesian team, prior to independence in 1945. Indonesia was the first Asian team to participate in the FIFA World Cup when the team qualified for the 1938 tournament after its opponent, Japan, withdrew from the qualification heats. The 6–0 loss to eventual finalists Hungary in the first round of the tournament in Reims, France, remains the nation's only appearance in the World Cup. The straight knock-out format used at the time made it the only game ever played by the Indonesians.

This is the complete list of Asian nations in FIFA World Cup:
Source : FIFA.com | Wikipedia.com