Often this verse is terribly misquoted by various groups within the Charismatic movement.
Taken out of context, the implication is that a person can be a believer and yet not have the Holy Ghost.
In the context however, note that these men were entirely unaware of the finished work of Jesus Christ
upon the cross. They were not believers in the gospel of Jesus Christ, but merely believers in the gospel
of John the Baptist – that a Messiah would one day be coming. Having never put their faith in the finished
work of Jesus Christ, they were not saved from their sins in the NT sense of the word until verse five
when they were duly informed of the facts by Paul. Beware of Acts 19:2 being twisted from its context.