All particles in the standard model are predicted to have an anti-particle that is identical in mass but has an opposite charge (e.g. electron and its anti-particle, the positron). Particles that have zero charge are thought to be their own anti-particle. There is, however, a large imbalance with relatively small quantities of anti-matter.
Particles can be converted into anti-particles, and vice versa. The rate of particle-to-antiparticle conversion should be equal to the rate of antiparticle-to-particle conversion. However, the rates are not always the same e.g. when it involves release of W bosons. This is the so-called charge parity (CP) violation and is neither predicted nor explained by the Standard Model. Unfortunately, it is not sufficient to explain the imbalance of matter and anti-matter in the universe.