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.
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