My afp level increased from 12.15 ng/ml to 12.90 ng/ml in two months. is this normal and what might cause an increase such as this?

Not enough for a trend, specifically if not checked for a known condition. Such values can only be interpreted in clinical context and the doc ordering the test has the best view in trying to draw a conclusion.

This rise in AFP is considered insignificant. Although high, an AFP rising by less than 1.0 over two months is minuscule; I would consider this as stable.