Police said they didn't suspect foul play.
"There were some drugs found around the body -- prescription-type drugs," a police spokesman told People.com.
TMZ.com reported Ledger, 28, was suffering from pneumonia when he died.
The celebrity news Web site also said it was contacted by a representative for Ledger's family who said they were upset by suggestions in the media that Ledger might have committed suicide.
The spokesperson said police told Ledger's family his death was accidental and there is no evidence to support rumors he may have taken his own life.
The actor starred in "Monster's Ball," "A Knight's Tale," "The Patriot," "10 Things I Hate About You" and "Ned Kelly." His role in the critically acclaimed 2005's "Brokeback Mountain," for which he earned an Oscar nomination, made him an A-list star.
The Perth, Australia, native is in the current release "I'm Not There" and his portrayal of the Joker in the upcoming Warner Bros. movie "The Dark Knight" has been generating buzz on fan Web sites for months.
Ledger and Michelle Williams, his co-star in "Brokeback Mountain," have a 2-year-old daughter.