A mutation that converts an amino acid codon to a stop codon is a:
Changes one codon for an amino acid into another codon for that same amino acid - Silent mutation
Codon for one amino acid is changed into a codon of another amino acid - Missense mutation
Codon for one amino acid is changed into a translation termination codon - Non-sense mutation
Reading frame changes downstream to the mutant site - Frameshift mutation.
A purine base replaced by another pyrimidine,  or  pyrimidine  replaced  by  another purine -Transversion.

Key Concept
Nonsense mutation
A coding codon mutated to a nonsense codon result in premature termination of polypeptide chain.
Nonsense mutation
Transversion
Silent mutation
Frame shift mutation