We report on the observation of bottom-charm mesons via the decay
mode B^+/-_c -> J/psi l^+/- nu in 1.8 TeV ppbar collisions using the CDF
detector at the Fermilab Tevatron.  A fit of background and signal
contributions to the J/psi l mass distribution yielded 20.4^+6.2_ -5.5 events
from B_c mesons.  We measured the B^+_c mass to be 6.40 +/- 0.39(stat.) +/-
0.13(syst.) GeV/c^2 and the B^+_c lifetime to be 0.46^+0.18_-0.16(stat.) +/-
0.03(syst.) ps.  The measured production cross section times branching ratio
for B^+_c -> J/psi l^+ nu relative to that for B^+ -> J/psi K^+ is
0.132^+0.041_ -0.037(stat.) +/- 0.031(syst.)^+0.032_-0.020(lifetime).