Although not one of the original Twelve Apostles, Barnabas was referred to as an apostle by the early Christian Church (Acts 14:14.) There is also a Church tradition which says that Barnabas was "first of the Seventy disciples of our Lord," however, this cannot be proven.
Having been ordained along with the apostle Paul for their first missionary journey by the church in Antioch, both Barnabas and Paul enjoyed the title and dignity of Apostles from that time forward (this took place around 45AD); this missionary journey was confined to Cyprus and Asia Minor which is well documented in the New Testament book of Acts.
On Barnabas' second missionary journey, he and John Mark returned to Cyprus; the Church of Cyprus had been founded by the apostles Barnabas and Paul on their first missionary journey.
During this missionary journey, Barnabas suffered death in his native town of Salamis on Cyprus and was buried secretively by John Mark; it's also interesting to note that John Mark was a relative of Barnabas.
The information above is compiled from the book "The Search for the Twelve Apostles" by William Steuart McBirnie Ph.D, Copyright 1973