A search for the lepton-flavor violating decays
B
+
→
K
+
μ
±
e
∓
is performed using a sample of proton-proton collision data, collected with the LHCb experiment at center-of-mass energies of 7 and 8 TeV and corresponding to an integrated luminosity of
3
 
 
fb
−
1
. No significant signal is observed, and upper limits on the branching fractions are set as
B
(
B
+
→
K
+
μ
−
e
+
)
<
7.0
(
9.5
)
×
10
−
9
and
B
(
B
+
→
K
+
μ
+
e
−
)
<
6.4
(
8.8
)
×
10
−
9
at 90% (95)% confidence level. The results improve the current best limits on these decays by more than one order of magnitude.