Ljungberg was born on 16 April 1977 in Vittsjö to Roy Alve Erling Ljungberg, a civil engineer and owner of a construction and consultant business, and Elisabeth Bodil Ljungberg, a Swedish Labor Department worker. On 12 September 1984, the Ljungbergs had another son, Karl Oskar Filip. In 1982, the Ljungberg family left Vittsjö and moved to Halmstad. At first, the tenacious five-year old would not have any part of moving. He argued with his parents that he did not want to live in Halmstad. His parents relented and took him to Halmstads BK, where he played on the youth team under manager Olle Eriksson.