The first-century historian Josephus reports that Jesus was a sage who performed wonders. This is a non-Christian source from Jesus’s era.
Some internet detractors demand eyewitness reports from the first century before they will believe, but such a demand displays historiographic ignorance because by this standard we would know almost nothing about ancient history. We have the next-best thing: sources from the first generation, including some who consulted eyewitnesses (Luke 1:1-2).
Suffice it to say that unless critics invent special standards for Jesus that we do not apply to the rest of ancient history, we know quite a lot about him. As for eyewitness testimonies of miracles, we not only have sources from within a generation of Jesus’s ministry, but we do have eyewitness accounts of his followers performing miracles, such as in Acts’ “we” section, Paul’s appeal to the Corinthians’ eyewitness experience of his miracles, eyewitness accounts in the church fathers, and millions of eyewitness claims today. But that is, again, another story.
Additional Resources on Contemporary Miracle Accounts
Dr. Keener received his Ph.D. in New Testament Studies and Christian Origins from Duke University. He is currently a professor of New Testament at Asbury Theological Seminary. He is especially known for his work in New Testament background (commentaries on the New Testament in its early Jewish and Greco-Roman settings). His award-winning, popular-level IVP Bible Background Commentary: New Testament has sold over half a million copies.