An unlawful arrest, by itself, will not result in the dismissal of the charges against you. Another way of saying this is that the unlawful arrest is not a defense that you can use at trial.

Of course, evidence that the police may have seized during the unlawful arrest should be suppressed in most situations. Depending on how crucial this evidence is to the prosecution's case, this may have a serious impact on the prosecutor's ability to go forward. For example, suppose an unlawful arrest resulted in a search of the defendant, which turned up a smoking gun. If the gun would not have been discovered in the due course of police work,  the gun will be kept out of evidence. The prosecutor may choose not to proceed if there is no other evidence linking the defendant to the crime.