Rob Bradshaw of the ever-helpful biblicalstudies.org.uk posts the following that may be of interest:

F.P. Cotterell, "The Gospel of Barnabas," Vox Evangelica 10 (1977): 43-47.

Here's the first paragraph:

The Gospel of Barnabas is one of three, or more precisely four, writings associated with the name of Paul’s companion in the first part of his mission to the gentiles. The earliest of these writings is the Epistle of Barnabas, dating from the first half of the second century. The Acts of Barnabas, a more convenient appellation than the formal Greek title, The journeys and the testimony of St. Barnabas the apostle, dates from the fifth century. Then there is the Gospel of Barnabas, a title which is confusingly applied to two works. The first of these is known to us only by name. It is referred to in the Latin Decretum Gelasianum, associated with pope Gelasius (492-496). Of the text of this Gospel we have no knowledge whatever. The second Gospel of Barnabas made its appearance in the sixteenth century and has re-surfaced at intervals ever since, most recently through a series of publications originating in Karachi, edited by Begum Aisha Bawany Wakf. This brief note is intended simply to draw attention to the character of the ‘Gospel’, to record what is known of its antecedents and the claims made for it by some Muslim apologists.

So if you have interest in such things, read the whole article.