A Perth man has been fined more than $6000 for illegally importing an unfinished firearm "silencer" he purchased online from a US-based website.

The 42-year-old pleaded guilty in the Perth Magistrates Court on Thursday to one charge under section 233(1)(b) of the Customs Act.

The silencer which landed the man in hot water. Credit:ABF

He was fined $6533.

Australian Border Force WA Regional Commander Rod O'Donnell said the penalty should serve as a reminder to people about the dangers of purchasing weapons or accessories online.