  We study the non-thermal jet emission of the BL Lac object B3 2247+381 during
a high optical state. The MAGIC telescopes observed the source during 13 nights
between September 30th and October 30th 2010, collecting a total of 14.2 hours
of good quality very high energy (VHE) $\gamma$-ray data. Simultaneous
multiwavelength data was obtained with X-ray observations by the Swift
satellite and optical R-band observations at the KVA-telescope. We also use
high energy $\gamma$-ray (HE, 0.1 GeV-100 GeV) data from the Fermi satellite.
The BL Lac object B3 2247+381 (z=0.119) was detected, for the first time, at
VHE $\gamma$-rays at a statistical significance of 5.6 $\sigma$. A soft VHE
spectrum with a photon index of -3.2 $\pm$ 0.6 was determined. No significant
short term flux variations were found. We model the spectral energy
distribution using a one-zone SSC-model, which can successfully describe our
data.
